diff --git a/core/CMakeLists.txt b/core/CMakeLists.txt
index 9d8cdb9f8..ca51fd50c 100644
--- a/core/CMakeLists.txt
+++ b/core/CMakeLists.txt
@@ -141,8 +141,9 @@ target_compile_definitions(reactor-c PRIVATE INITIAL_EVENT_QUEUE_SIZE=${INITIAL_
 target_compile_definitions(reactor-c PRIVATE INITIAL_REACT_QUEUE_SIZE=${INITIAL_REACT_QUEUE_SIZE})
 target_compile_definitions(reactor-c PUBLIC PLATFORM_${CMAKE_SYSTEM_NAME})
 
-# Macro for translating a command-line argument into compile definition for
-# reactor-c lib
+# If variable X is defined in cMake (set using SET()) or passed in as a command-line
+# argument using -DX=<value>, then make it a compiler flag for reactor-c so that X
+# is also defined in the C code for reactor-c.
 macro(define X)
     if(DEFINED ${X})
         message(STATUS ${X}=${${X}})
@@ -155,8 +156,7 @@ message(STATUS "Applying preprocessor definitions...")
 define(_LF_CLOCK_SYNC_ATTENUATION)
 define(_LF_CLOCK_SYNC_COLLECT_STATS)
 define(_LF_CLOCK_SYNC_EXCHANGES_PER_INTERVAL)
-define(_LF_CLOCK_SYNC_INITIAL)
-define(_LF_CLOCK_SYNC_ON)
+define(LF_CLOCK_SYNC) # 1 for OFF, 2 for INIT and 3 for ON.
 define(_LF_CLOCK_SYNC_PERIOD_NS)
 define(_LF_FEDERATE_NAMES_COMMA_SEPARATED)
 define(ADVANCE_MESSAGE_INTERVAL)
diff --git a/core/clock.c b/core/clock.c
index cdebaefde..8b10297a7 100644
--- a/core/clock.c
+++ b/core/clock.c
@@ -8,13 +8,14 @@
 #include "clock.h"
 #include "low_level_platform.h"
 
-#if defined(_LF_CLOCK_SYNC_ON) || defined(_LF_CLOCK_SYNC_INITIAL)
+// If we are federated, include clock-sync API (and implementation)
+#if defined(FEDERATED)
 #include "clock-sync.h"
 #else
-// Provide empty implementations of these functions.
+// In the unfederated case, just provide empty implementations.
 void clock_sync_add_offset(instant_t* t) { (void)t; }
 void clock_sync_subtract_offset(instant_t* t) { (void)t; }
-#endif // defined(_LF_CLOCK_SYNC_ON) || defined(_LF_CLOCK_SYNC_INITIAL)
+#endif // defined(FEDERATED)
 
 static instant_t last_read_physical_time = NEVER;
 
diff --git a/core/federated/RTI/rti_remote.c b/core/federated/RTI/rti_remote.c
index a88f384c4..cc0252843 100644
--- a/core/federated/RTI/rti_remote.c
+++ b/core/federated/RTI/rti_remote.c
@@ -1738,9 +1738,14 @@ void initialize_RTI(rti_remote_t* rti) {
   rti_remote->stop_in_progress = false;
 }
 
+// The RTI includes clock.c, which requires the following functions that are defined
+// in clock-sync.c.  But clock-sync.c is not included in the standalone RTI.
+// Provide empty implementations of these functions.
+void clock_sync_add_offset(instant_t* t) { (void)t; }
+void clock_sync_subtract_offset(instant_t* t) { (void)t; }
+
 void free_scheduling_nodes(scheduling_node_t** scheduling_nodes, uint16_t number_of_scheduling_nodes) {
   for (uint16_t i = 0; i < number_of_scheduling_nodes; i++) {
-    // FIXME: Gives error freeing memory not allocated!!!!
     scheduling_node_t* node = scheduling_nodes[i];
     if (node->upstream != NULL)
       free(node->upstream);
diff --git a/core/federated/clock-sync.c b/core/federated/clock-sync.c
index 2a6ce8e3d..b18efb650 100644
--- a/core/federated/clock-sync.c
+++ b/core/federated/clock-sync.c
@@ -161,8 +161,8 @@ void reset_socket_stat(struct socket_stat_t* socket_stat) {
  *   will be sent.
  */
 uint16_t setup_clock_synchronization_with_rti() {
-  uint16_t port_to_return = UINT16_MAX;
-#ifdef _LF_CLOCK_SYNC_ON
+  uint16_t port_to_return = UINT16_MAX; // Default if clock sync is off.
+#if (LF_CLOCK_SYNC >= LF_CLOCK_SYNC_ON)
   // Initialize the UDP socket
   _lf_rti_socket_UDP = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
   // Initialize the necessary information for the UDP address
@@ -201,11 +201,9 @@ uint16_t setup_clock_synchronization_with_rti() {
   if (setsockopt(_lf_rti_socket_UDP, SOL_SOCKET, SO_SNDTIMEO, (const char*)&timeout_time, sizeof(timeout_time)) < 0) {
     lf_print_error("Failed to set SO_SNDTIMEO option on the socket: %s.", strerror(errno));
   }
-#else // No runtime clock synchronization. Send port -1 or 0 instead.
-#ifdef _LF_CLOCK_SYNC_INITIAL
+#elif (LF_CLOCK_SYNC == LF_CLOCK_SYNC_INIT)
   port_to_return = 0u;
-#endif // _LF_CLOCK_SYNC_INITIAL
-#endif // _LF_CLOCK_SYNC_ON
+#endif // (LF_CLOCK_SYNC >= LF_CLOCK_SYNC_ON)
   return port_to_return;
 }
 
@@ -530,17 +528,21 @@ void* listen_to_rti_UDP_thread(void* args) {
 
 // If clock synchronization is enabled, provide implementations. If not
 // just empty implementations that should be optimized away.
-#if defined(_LF_CLOCK_SYNC_ON) || defined(_LF_CLOCK_SYNC_INITIAL)
-void clock_sync_add_offset(instant_t* t) { *t += (_lf_clock_sync_offset + _lf_clock_sync_constant_bias); }
+#if (LF_CLOCK_SYNC >= LF_CLOCK_SYNC_INIT)
+void clock_sync_add_offset(instant_t* t) {
+  *t = lf_time_add(*t, (_lf_clock_sync_offset + _lf_clock_sync_constant_bias));
+}
 
-void clock_sync_subtract_offset(instant_t* t) { *t -= (_lf_clock_sync_offset + _lf_clock_sync_constant_bias); }
+void clock_sync_subtract_offset(instant_t* t) {
+  *t = lf_time_add(*t, -(_lf_clock_sync_offset + _lf_clock_sync_constant_bias));
+}
 
 void clock_sync_set_constant_bias(interval_t offset) { _lf_clock_sync_constant_bias = offset; }
-#else
-// Empty implementations of clock_sync_add_offset and clock_sync_subtract_offset
-// are in clock.c.
+#else  // i.e. (LF_CLOCK_SYNC < LF_CLOCK_SYNC_INIT)
+void clock_sync_add_offset(instant_t* t) { (void)t; }
+void clock_sync_subtract_offset(instant_t* t) { (void)t; }
 void clock_sync_set_constant_bias(interval_t offset) { (void)offset; }
-#endif // (defined(_LF_CLOCK_SYNC_ON) || defined(_LF_CLOCK_SYNC_INITIAL)
+#endif // (LF_CLOCK_SYNC >= LF_CLOCK_SYNC_INIT)
 
 /**
  * Create the thread responsible for handling clock synchronization
@@ -551,12 +553,12 @@ void clock_sync_set_constant_bias(interval_t offset) { (void)offset; }
  * \ingroup agroup
  */
 int create_clock_sync_thread(lf_thread_t* thread_id) {
-#ifdef _LF_CLOCK_SYNC_ON
+#if (LF_CLOCK_SYNC >= LF_CLOCK_SYNC_ON)
   // One for UDP messages if clock synchronization is enabled for this federate
   return lf_thread_create(thread_id, listen_to_rti_UDP_thread, NULL);
-#else
-  (void)thread_id;
-#endif // _LF_CLOCK_SYNC_ON
+#else  // i.e. (LF_CLOCK_SYNC < LF_CLOCK_SYNC_ON)
+  (void)thread_id; // Suppress unused parameter warning.
+#endif // (LF_CLOCK_SYNC >= LF_CLOCK_SYNC_ON)
   return 0;
 }
 
diff --git a/core/reactor_common.c b/core/reactor_common.c
index dd348a52a..3f337ea6a 100644
--- a/core/reactor_common.c
+++ b/core/reactor_common.c
@@ -1187,6 +1187,8 @@ void termination(void) {
 #endif
     lf_free_all_reactors();
 
+    lf_tracing_global_shutdown();
+
     // Free up memory associated with environment.
     // Do this last so that printed warnings don't access freed memory.
     for (int i = 0; i < num_envs; i++) {
@@ -1196,7 +1198,6 @@ void termination(void) {
     free_local_rti();
 #endif
   }
-  lf_tracing_global_shutdown();
 }
 
 index_t lf_combine_deadline_and_level(interval_t deadline, int level) {
diff --git a/core/tag.c b/core/tag.c
index 9bb35933f..c5f8f88c6 100644
--- a/core/tag.c
+++ b/core/tag.c
@@ -39,20 +39,46 @@ tag_t lf_tag(void* env) {
   return ((environment_t*)env)->current_tag;
 }
 
+instant_t lf_time_add(instant_t a, interval_t b) {
+  if (a == NEVER || b == NEVER) {
+    return NEVER;
+  }
+  if (a == FOREVER || b == FOREVER) {
+    return FOREVER;
+  }
+  instant_t res = a + b;
+  // Check for overflow
+  if (res < a && b > 0) {
+    return FOREVER;
+  }
+  // Check for underflow
+  if (res > a && b < 0) {
+    return NEVER;
+  }
+  return res;
+}
+
 tag_t lf_tag_add(tag_t a, tag_t b) {
-  if (a.time == NEVER || b.time == NEVER)
-    return NEVER_TAG;
-  if (a.time == FOREVER || b.time == FOREVER)
+  instant_t res = lf_time_add(a.time, b.time);
+  if (res == FOREVER) {
     return FOREVER_TAG;
-  if (b.time > 0)
+  }
+  if (res == NEVER) {
+    return NEVER_TAG;
+  }
+
+  if (b.time > 0) {
+    // NOTE: The reason for handling this case is to "reset" the microstep counter at each after delay.
     a.microstep = 0; // Ignore microstep of first arg if time of second is > 0.
-  tag_t result = {.time = a.time + b.time, .microstep = a.microstep + b.microstep};
-  if (result.microstep < a.microstep)
-    return FOREVER_TAG;
-  if (result.time < a.time && b.time > 0)
+  }
+  tag_t result = {.time = res, .microstep = a.microstep + b.microstep};
+
+  // If microsteps overflows
+  // FIXME: What should be the resulting tag in case of microstep overflow.
+  //  see https://github.com/lf-lang/reactor-c/issues/430
+  if (result.microstep < a.microstep) {
     return FOREVER_TAG;
-  if (result.time > a.time && b.time < 0)
-    return NEVER_TAG;
+  }
   return result;
 }
 
diff --git a/include/core/federated/clock-sync.h b/include/core/federated/clock-sync.h
index 9c9de110d..b003a3150 100644
--- a/include/core/federated/clock-sync.h
+++ b/include/core/federated/clock-sync.h
@@ -35,6 +35,15 @@ THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 #include "low_level_platform.h"
 
+// Clock synchronization defaults to performing clock synchronization only at initialization.
+#define LF_CLOCK_SYNC_OFF 1
+#define LF_CLOCK_SYNC_INIT 2
+#define LF_CLOCK_SYNC_ON 3
+
+#ifndef LF_CLOCK_SYNC
+#define LF_CLOCK_SYNC LF_CLOCK_SYNC_INIT
+#endif
+
 /**
  * Number of required clock sync T4 messages per synchronization
  * interval. The offset to the clock will not be adjusted until
diff --git a/tag/api/tag.h b/tag/api/tag.h
index c903aaf53..c40e490f8 100644
--- a/tag/api/tag.h
+++ b/tag/api/tag.h
@@ -104,6 +104,15 @@ tag_t lf_tag(void* env);
  */
 tag_t lf_tag_add(tag_t a, tag_t b);
 
+/**
+ * @brief Return the sum of an interval and an instant, saturating on overflow and underflow.
+ *
+ * @param a
+ * @param b
+ * @return instant_t
+ */
+instant_t lf_time_add(instant_t a, interval_t b);
+
 /**
  * Compare two tags. Return -1 if the first is less than
  * the second, 0 if they are equal, and +1 if the first is