diff --git a/indra/llcommon/llstring.cpp b/indra/llcommon/llstring.cpp
index bcd5e30b1e..efc9cb6180 100644
--- a/indra/llcommon/llstring.cpp
+++ b/indra/llcommon/llstring.cpp
@@ -1070,6 +1070,7 @@ std::optional<std::string> llstring_getoptenv(const std::string& key)
 long LLStringOps::sPacificTimeOffset = 0;
 long LLStringOps::sLocalTimeOffset = 0;
 bool LLStringOps::sPacificDaylightTime = 0;
+bool LLStringOps::sUsingPacificTime = false; // <FS:TJ/> [FIRE-34775] Use PST/PDT when logged into OpenSim
 std::map<std::string, std::string> LLStringOps::datetimeToCodes;
 
 std::vector<std::string> LLStringOps::sWeekDayList;
@@ -1628,12 +1629,21 @@ bool LLStringUtil::formatDatetime(std::string& replacement, std::string token,
         }
         else
         {
-#if 0
+// <FS:TJ> [FIRE-34775] Use PST/PDT when logged into OpenSim
+#ifdef OPENSIM
             // EXT-1565 : Zai Lynch, James Linden : 15/Oct/09
             // [BSI] Feedback: Viewer clock mentions SLT, but would prefer it to show PST/PDT
             // "slt" = Second Life Time, which is deprecated.
             // If not utc or user local time, fallback to Pacific time
-            replacement = LLStringOps::getPacificDaylightTime() ? "PDT" : "PST";
+            if (LLStringOps::getUsingPacificTime())
+            {
+                replacement = LLStringOps::getPacificDaylightTime() ? "PDT" : "PST";
+            }
+            else
+            {
+                replacement = "SLT";
+            }
+// </FS:TJ>
 #else
             // SL-20370 : Steeltoe Linden : 29/Sep/23
             // Change "PDT" to "SLT" on menu bar
diff --git a/indra/llcommon/llstring.h b/indra/llcommon/llstring.h
index 07615aa027..9375534f3c 100644
--- a/indra/llcommon/llstring.h
+++ b/indra/llcommon/llstring.h
@@ -153,6 +153,7 @@ private:
     static long sPacificTimeOffset;
     static long sLocalTimeOffset;
     static bool sPacificDaylightTime;
+    static bool sUsingPacificTime; // <FS:TJ/> [FIRE-34775] Use PST/PDT when logged into OpenSim
 
     static std::map<std::string, std::string> datetimeToCodes;
 
@@ -204,6 +205,9 @@ public:
     static S32  collate(const llwchar* a, const llwchar* b);
 
     static void setupDatetimeInfo(bool pacific_daylight_time);
+    // <FS:TJ> [FIRE-34775] Use PST/PDT when logged into OpenSim
+    static void setupUsingPacificTime(bool use_pacific_time) { sUsingPacificTime = use_pacific_time; }
+    // </FS:TJ>
 
     static void setupWeekDaysNames(const std::string& data);
     static void setupWeekDaysShortNames(const std::string& data);
@@ -217,6 +221,9 @@ public:
     // Is the Pacific time zone (aka server time zone)
     // currently in daylight savings time?
     static bool getPacificDaylightTime(void) { return sPacificDaylightTime;}
+    // <FS:TJ> [FIRE-34775] Use PST/PDT when logged into OpenSim
+    static bool getUsingPacificTime() { return sUsingPacificTime; }
+    // </FS:TJ>
 
     static std::string getDatetimeCode (std::string key);
 
diff --git a/indra/newview/llstartup.cpp b/indra/newview/llstartup.cpp
index c693c9ff25..8781a34a04 100644
--- a/indra/newview/llstartup.cpp
+++ b/indra/newview/llstartup.cpp
@@ -4875,6 +4875,9 @@ bool process_login_success_response(U32 &first_sim_size_x, U32 &first_sim_size_y
 
         //setup map of datetime strings to codes and slt & local time offset from utc
         LLStringOps::setupDatetimeInfo(pacific_daylight_time);
+        // <FS:TJ> [FIRE-34775] Use PST/PDT when logged into OpenSim
+        LLStringOps::setupUsingPacificTime(LLGridManager::getInstance()->isInOpenSim());
+        // </FS:TJ>
     }
 
     // set up the voice configuration.  Ultimately, we should pass this up as part of each voice