diff --git a/indra/newview/app_settings/settings.xml b/indra/newview/app_settings/settings.xml
index a0c0f15b88..b281066e7d 100644
--- a/indra/newview/app_settings/settings.xml
+++ b/indra/newview/app_settings/settings.xml
@@ -21448,6 +21448,17 @@ Change of this parameter will affect the layout of buttons in notification toast
     <key>Value</key>
     <integer>0</integer>
   </map>
+  <key>FSEnvironmentManualTransitionTime</key>
+  <map>
+    <key>Comment</key>
+    <string>Timespan for blending between day/water/sky settings when manually changed. 0 is immediate.</string>
+    <key>Persist</key>
+    <integer>1</integer>
+    <key>Type</key>
+    <string>F32</string>
+    <key>Value</key>
+    <real>0.0</real>
+  </map>
   <key>FSDisableAvatarTrackerAtCloseIn</key>
   <map>
     <key>Comment</key>
diff --git a/indra/newview/llenvironment.cpp b/indra/newview/llenvironment.cpp
index a850d1bbda..d818c454ab 100644
--- a/indra/newview/llenvironment.cpp
+++ b/indra/newview/llenvironment.cpp
@@ -1283,12 +1283,33 @@ void LLEnvironment::setEnvironment(EnvSelection_t env, const LLUUID &assetId, S3
     setEnvironment(env, assetId, LLSettingsDay::DEFAULT_DAYLENGTH, LLSettingsDay::DEFAULT_DAYOFFSET);
 }
 
-
-void LLEnvironment::setEnvironment(EnvSelection_t env,
-                                   const LLUUID &assetId,
-                                   LLSettingsDay::Seconds daylength,
-                                   LLSettingsDay::Seconds dayoffset,
-                                   S32 env_version)
+// <FS:Beq> FIRE-29926 - allow manually selected environments to have a user defined transition time.
+void LLEnvironment::setManualEnvironment(EnvSelection_t env, const LLUUID &assetId, S32 env_version)
+{
+    LLSettingsBase::Seconds transitionTime(static_cast<F64>(gSavedSettings.getF32("FSEnvironmentManualTransitionTime")));
+    setEnvironmentWithTransition(env, assetId, LLSettingsDay::DEFAULT_DAYLENGTH, LLSettingsDay::DEFAULT_DAYOFFSET, transitionTime);
+}
+void LLEnvironment::setEnvironmentWithTransition(
+                                    EnvSelection_t env,
+                                    const LLUUID &assetId,
+                                    LLSettingsDay::Seconds daylength,
+                                    LLSettingsDay::Seconds dayoffset,
+                                    LLSettingsBase::Seconds transition,
+                                    S32 env_version)
+{
+    LLSettingsVOBase::getSettingsAsset(assetId,
+        [this, env, daylength, dayoffset, transition, env_version](LLUUID asset_id, LLSettingsBase::ptr_t settings, S32 status, LLExtStat)
+        {
+            onSetEnvAssetLoaded(env, asset_id, settings, daylength, dayoffset, transition, status, env_version);
+        });
+}
+// </FS:Beq>
+void LLEnvironment::setEnvironment(
+                                    EnvSelection_t env,
+                                    const LLUUID &assetId,
+                                    LLSettingsDay::Seconds daylength,
+                                    LLSettingsDay::Seconds dayoffset,
+                                    S32 env_version)
 {
     LLSettingsVOBase::getSettingsAsset(assetId,
         [this, env, daylength, dayoffset, env_version](LLUUID asset_id, LLSettingsBase::ptr_t settings, S32 status, LLExtStat)
diff --git a/indra/newview/llenvironment.h b/indra/newview/llenvironment.h
index bbd0adaca8..a974e3893c 100644
--- a/indra/newview/llenvironment.h
+++ b/indra/newview/llenvironment.h
@@ -145,6 +145,10 @@ public:
     void                        setEnvironment(EnvSelection_t env, const LLSettingsWater::ptr_t & fixed, S32 env_version = NO_VERSION) { setEnvironment(env, fixedEnvironment_t(LLSettingsSky::ptr_t(), fixed), env_version); }
     void                        setEnvironment(EnvSelection_t env, const LLSettingsSky::ptr_t & fixeds, const LLSettingsWater::ptr_t & fixedw, S32 env_version = NO_VERSION) { setEnvironment(env, fixedEnvironment_t(fixeds, fixedw), env_version); }
     void                        setEnvironment(EnvSelection_t env, const LLUUID &assetId, LLSettingsDay::Seconds daylength, LLSettingsDay::Seconds dayoffset, S32 env_version = NO_VERSION);
+    // <FS:Beq> FIRE-29926 - Allow configurable transition times
+    void                        setEnvironmentWithTransition(EnvSelection_t env, const LLUUID &assetId, LLSettingsDay::Seconds daylength, LLSettingsDay::Seconds dayoffset, LLSettingsBase::Seconds transition, S32 env_version = NO_VERSION);
+    void                        setManualEnvironment(EnvSelection_t env, const LLUUID &assetId, S32 env_version = NO_VERSION);
+    // </FS:Beq>
     void                        setEnvironment(EnvSelection_t env, const LLUUID &assetId, S32 env_version = NO_VERSION);
 
     void                        setSharedEnvironment();
diff --git a/indra/newview/llviewermenu.cpp b/indra/newview/llviewermenu.cpp
index 74d5277ce9..f18e75d948 100644
--- a/indra/newview/llviewermenu.cpp
+++ b/indra/newview/llviewermenu.cpp
@@ -10800,28 +10800,40 @@ class LLWorldEnvSettings : public view_listener_t
 		
 		if (event_name == "sunrise")
 		{
-            LLEnvironment::instance().setEnvironment(LLEnvironment::ENV_LOCAL, LLEnvironment::KNOWN_SKY_SUNRISE);
+			// <FS:Beq> FIRE-29926 - allow manually selected environments to have a user defined transition time.
+			// LLEnvironment::instance().setEnvironment(LLEnvironment::ENV_LOCAL, LLEnvironment::KNOWN_SKY_SUNRISE);
+            LLEnvironment::instance().setManualEnvironment(LLEnvironment::ENV_LOCAL, LLEnvironment::KNOWN_SKY_SUNRISE);
+			// </FS:Beq>
             LLEnvironment::instance().setSelectedEnvironment(LLEnvironment::ENV_LOCAL);
             LLEnvironment::instance().updateEnvironment();
             defocusEnvFloaters();
 		}
 		else if (event_name == "noon")
 		{
-            LLEnvironment::instance().setEnvironment(LLEnvironment::ENV_LOCAL, LLEnvironment::KNOWN_SKY_MIDDAY);
+			// <FS:Beq> FIRE-29926 - allow manually selected environments to have a user defined transition time.
+            // LLEnvironment::instance().setEnvironment(LLEnvironment::ENV_LOCAL, LLEnvironment::KNOWN_SKY_MIDDAY);
+            LLEnvironment::instance().setManualEnvironment(LLEnvironment::ENV_LOCAL, LLEnvironment::KNOWN_SKY_MIDDAY);
+			// </FS:Beq>
             LLEnvironment::instance().setSelectedEnvironment(LLEnvironment::ENV_LOCAL);
             LLEnvironment::instance().updateEnvironment();
             defocusEnvFloaters();
 		}
 		else if (event_name == "sunset")
 		{
-            LLEnvironment::instance().setEnvironment(LLEnvironment::ENV_LOCAL, LLEnvironment::KNOWN_SKY_SUNSET);
+			// <FS:Beq> FIRE-29926 - allow manually selected environments to have a user defined transition time.
+            // LLEnvironment::instance().setEnvironment(LLEnvironment::ENV_LOCAL, LLEnvironment::KNOWN_SKY_SUNSET);
+            LLEnvironment::instance().setManualEnvironment(LLEnvironment::ENV_LOCAL, LLEnvironment::KNOWN_SKY_SUNSET);
+			// </FS:Beq>
             LLEnvironment::instance().setSelectedEnvironment(LLEnvironment::ENV_LOCAL);
             LLEnvironment::instance().updateEnvironment();
             defocusEnvFloaters();
 		}
 		else if (event_name == "midnight")
 		{
-            LLEnvironment::instance().setEnvironment(LLEnvironment::ENV_LOCAL, LLEnvironment::KNOWN_SKY_MIDNIGHT);
+			// <FS:Beq> FIRE-29926 - allow manually selected environments to have a user defined transition time.
+            // LLEnvironment::instance().setEnvironment(LLEnvironment::ENV_LOCAL, LLEnvironment::KNOWN_SKY_MIDNIGHT);
+            LLEnvironment::instance().setManualEnvironment(LLEnvironment::ENV_LOCAL, LLEnvironment::KNOWN_SKY_MIDNIGHT);
+			// </FS:Beq>
             LLEnvironment::instance().setSelectedEnvironment(LLEnvironment::ENV_LOCAL);
             LLEnvironment::instance().updateEnvironment();
             defocusEnvFloaters();
diff --git a/indra/newview/quickprefs.cpp b/indra/newview/quickprefs.cpp
index 6334549f51..75c9b7e893 100644
--- a/indra/newview/quickprefs.cpp
+++ b/indra/newview/quickprefs.cpp
@@ -827,6 +827,8 @@ void FloaterQuickPrefs::selectSkyPreset(const LLSD& preset)
 			// Need to preserve current sky manually in this case in contrast to asset-based settings
 			LLSettingsWater::ptr_t current_water = LLEnvironment::instance().getCurrentWater();
 			LLEnvironment::instance().setEnvironment(LLEnvironment::ENV_LOCAL, legacy_sky, current_water);
+			LLEnvironment::instance().setSelectedEnvironment(LLEnvironment::ENV_LOCAL);
+			LLEnvironment::instance().updateEnvironment(static_cast<LLSettingsBase::Seconds>(gSavedSettings.getF32("FSEnvironmentManualTransitionTime")));
 		}		
 		else
 		{
@@ -837,10 +839,10 @@ void FloaterQuickPrefs::selectSkyPreset(const LLSD& preset)
 	else // note the else here bridges the endif
 #endif
 	{
-		LLEnvironment::instance().setEnvironment(LLEnvironment::ENV_LOCAL, preset.asUUID());
+		LLEnvironment::instance().setSelectedEnvironment(LLEnvironment::ENV_LOCAL);
+		LLEnvironment::instance().setManualEnvironment(LLEnvironment::ENV_LOCAL, preset.asUUID());
 	}
-	LLEnvironment::instance().setSelectedEnvironment(LLEnvironment::ENV_LOCAL);
-	LLEnvironment::instance().updateEnvironment(LLEnvironment::TRANSITION_FAST, true);
+	// LLEnvironment::instance().updateEnvironment(LLEnvironment::TRANSITION_FAST);
 }
 
 void FloaterQuickPrefs::selectWaterPreset(const LLSD& preset)
@@ -856,6 +858,8 @@ void FloaterQuickPrefs::selectWaterPreset(const LLSD& preset)
 			// Need to preserve current sky manually in this case in contrast to asset-based settings
 			LLSettingsSky::ptr_t current_sky = LLEnvironment::instance().getCurrentSky();
 			LLEnvironment::instance().setEnvironment(LLEnvironment::ENV_LOCAL, current_sky, legacy_water);
+			LLEnvironment::instance().setSelectedEnvironment(LLEnvironment::ENV_LOCAL);
+			LLEnvironment::instance().updateEnvironment(static_cast<LLSettingsBase::Seconds>(gSavedSettings.getF32("FSEnvironmentManualTransitionTime")));
 		}		
 		else
 		{
@@ -866,10 +870,9 @@ void FloaterQuickPrefs::selectWaterPreset(const LLSD& preset)
 	else // beware the trailing else here.
 #endif
 	{
-		LLEnvironment::instance().setEnvironment(LLEnvironment::ENV_LOCAL, preset.asUUID());
+		LLEnvironment::instance().setSelectedEnvironment(LLEnvironment::ENV_LOCAL);
+		LLEnvironment::instance().setManualEnvironment(LLEnvironment::ENV_LOCAL, preset.asUUID());
 	}
-	LLEnvironment::instance().setSelectedEnvironment(LLEnvironment::ENV_LOCAL);
-	LLEnvironment::instance().updateEnvironment(LLEnvironment::TRANSITION_FAST, true);
 }
 
 void FloaterQuickPrefs::selectDayCyclePreset(const LLSD& preset)
@@ -883,6 +886,8 @@ void FloaterQuickPrefs::selectDayCyclePreset(const LLSD& preset)
 		if (legacyday)
 		{
 			LLEnvironment::instance().setEnvironment(LLEnvironment::ENV_LOCAL, legacyday);
+			LLEnvironment::instance().setSelectedEnvironment(LLEnvironment::ENV_LOCAL);
+			LLEnvironment::instance().updateEnvironment(static_cast<LLSettingsBase::Seconds>(gSavedSettings.getF32("FSEnvironmentManualTransitionTime")));
 		}		
 		else
 		{
@@ -893,10 +898,9 @@ void FloaterQuickPrefs::selectDayCyclePreset(const LLSD& preset)
 	else // beware trailing else that bridges the endif
 #endif
 	{
-		LLEnvironment::instance().setEnvironment(LLEnvironment::ENV_LOCAL, preset.asUUID());
+		LLEnvironment::instance().setSelectedEnvironment(LLEnvironment::ENV_LOCAL);
+		LLEnvironment::instance().setManualEnvironment(LLEnvironment::ENV_LOCAL, preset.asUUID());
 	}
-	LLEnvironment::instance().setSelectedEnvironment(LLEnvironment::ENV_LOCAL);
-	LLEnvironment::instance().updateEnvironment(LLEnvironment::TRANSITION_FAST, true);
 }
 
 void FloaterQuickPrefs::onChangeWaterPreset()
diff --git a/indra/newview/skins/default/xui/en/panel_preferences_firestorm.xml b/indra/newview/skins/default/xui/en/panel_preferences_firestorm.xml
index 4cfb76e4c3..148ae17cd6 100644
--- a/indra/newview/skins/default/xui/en/panel_preferences_firestorm.xml
+++ b/indra/newview/skins/default/xui/en/panel_preferences_firestorm.xml
@@ -182,7 +182,22 @@
              name="flight_extreme"
              value="15.0" />
         </combo_box>
-
+        <slider
+        name="manual_environment_change_transition_period"
+        control_name="FSEnvironmentManualTransitionTime"
+        label="Environment Transition Time:"
+        decimal_digits="1"
+        left="10"
+        top_pad="5"
+        follows="left|top"
+        layout="topleft"
+        height="18"
+        increment="0.5"
+        initial_value="0"
+        max_val="60"
+        min_val="0"
+        width="520"
+        tool_tip="Interval in seconds over which manual environment changes will blend. Zero is instant."/>
     </panel>