diff --git a/core/reactor.c b/core/reactor.c
index d044a6ce6..71e58377f 100644
--- a/core/reactor.c
+++ b/core/reactor.c
@@ -328,16 +328,9 @@ int lf_reactor_c_main(int argc, const char* argv[]) {
 
     LF_PRINT_DEBUG("Initializing.");
     initialize_global();
-    // Set start time
-    if (!start_time_specified) {
-      start_time = lf_time_physical();
-    } else {
-      instant_t now = lf_time_physical();
-      if (now < start_time) {
-        LF_PRINT_LOG("Sleeping " PRINTF_TIME " ns until start time", start_time - now);
-        lf_sleep(start_time - now);
-      }
-    }
+    // Set the start time of the program (if it is not set from the command line). Possibly wait for
+    // it to arrive also.
+    _lf_set_and_wait_for_start_time();
 #ifndef FEDERATED
     lf_tracing_set_start_time(start_time);
 #endif
diff --git a/core/reactor_common.c b/core/reactor_common.c
index ca38cbaf3..ab0c07dd4 100644
--- a/core/reactor_common.c
+++ b/core/reactor_common.c
@@ -885,11 +885,11 @@ void usage(int argc, const char* argv[]) {
   printf("   Executed in <n> threads if possible (optional feature).\n\n");
   printf("  -i, --id <n>\n");
   printf("   The ID of the federation that this reactor will join.\n\n");
-  printf("  -s, --start-time <duration> <units> \n");
-  printf("   The logical start time of the program, expressed as a duration since the epoch of the underlying system "
-         "clock.\n");
+  printf("  -s, --start-time <time-point> <units> \n");
+  printf("   The logical start time of the program, expressed as an absolute time point\n");
+  printf("   which is the duration since the epoch of the underlying system clock.\n");
   printf("   The units are nsec, usec, msec, sec, minute, hour, day, week or the plurals of those.\n");
-  printf("   On linux, to compute a start time in 2 minutes you can do:.\n");
+  printf("   On linux, to compute a start time of 2 minutes into the future, expressed in seconds, do:\n");
   printf("     `date -d \"2 minutes\" +%%s`.\n\n");
 #ifdef FEDERATED
   printf("  -r, --rti <n>\n");
@@ -1261,3 +1261,15 @@ index_t lf_combine_deadline_and_level(interval_t deadline, int level) {
   else
     return (deadline << 16) | level;
 }
+
+void _lf_set_and_wait_for_start_time() {
+  if (!start_time_specified) {
+    start_time = lf_time_physical();
+  } else {
+    instant_t now = lf_time_physical();
+    if (!fast && now < start_time) {
+      lf_print("Sleeping " PRINTF_TIME " ns until specified start time", start_time - now);
+      lf_sleep(start_time - now);
+    }
+  }
+}
\ No newline at end of file
diff --git a/core/threaded/reactor_threaded.c b/core/threaded/reactor_threaded.c
index 5bc797ab0..d61973549 100644
--- a/core/threaded/reactor_threaded.c
+++ b/core/threaded/reactor_threaded.c
@@ -1017,15 +1017,9 @@ int lf_reactor_c_main(int argc, const char* argv[]) {
 
   // Initialize the clock through the platform API. No reading of physical time before this.
   _lf_initialize_clock();
-  if (!start_time_specified) {
-    start_time = lf_time_physical();
-  } else {
-    instant_t now = lf_time_physical();
-    if (now < start_time) {
-      LF_PRINT_LOG("Sleeping " PRINTF_TIME " ns until start time", start_time - now);
-      lf_sleep(start_time - now);
-    }
-  }
+  // Set the start time of the program (if it is not set from the command line). Possibly wait for
+  // it to arrive also.
+  _lf_set_and_wait_for_start_time();
 #ifndef FEDERATED
   lf_tracing_set_start_time(start_time);
 #endif
diff --git a/include/core/reactor_common.h b/include/core/reactor_common.h
index 1ff26733a..049672c22 100644
--- a/include/core/reactor_common.h
+++ b/include/core/reactor_common.h
@@ -66,6 +66,11 @@ extern struct allocation_record_t* _lf_reactors_to_free;
 
 //////////////////////  Functions  //////////////////////
 
+/**
+ * @brief Set the start time of the program and possibly wait for it to arrive.
+ */
+void _lf_set_and_wait_for_start_time();
+
 /**
  * @brief Combine a deadline and a level into a single index for sorting in the reaction queue.
  *