diff --git a/backend/app/activities/activity_streams/crud.py b/backend/app/activities/activity_streams/crud.py
index 64cdf302d..e1e32d864 100644
--- a/backend/app/activities/activity_streams/crud.py
+++ b/backend/app/activities/activity_streams/crud.py
@@ -425,14 +425,13 @@ def transform_activity_streams_hr(activity_stream, activity, db):
     ]
     zone_percentages = [round((count / total) * 100, 2) for count in zone_counts]
     
-    # Calculate time in seconds for each zone
-    # Use the same logic as percentage: distribute total_timer_time based on waypoint ratio
-    if hasattr(activity, 'total_timer_time') and activity.total_timer_time and total > 0:
+    # Calculate time in seconds for each zone using the percentage of total_timer_time
+    if hasattr(activity, 'total_timer_time') and activity.total_timer_time:
         total_time_seconds = activity.total_timer_time
-        zone_time_seconds = [int((count / total) * total_time_seconds) for count in zone_counts]
+        zone_time_seconds = [int((percent / 100) * total_time_seconds) for percent in zone_percentages]
     else:
-        # Fallback: assume waypoints represent equal time intervals
-        zone_time_seconds = [int(count) for count in zone_counts]
+        # Fallback: no time calculation possible without total_timer_time
+        zone_time_seconds = [0, 0, 0, 0, 0]
 
     # Calculate zone HR boundaries for display
     zone_hr = {
diff --git a/frontend/app/src/components/Activities/ActivityBellowMPillsComponent.vue b/frontend/app/src/components/Activities/ActivityBellowMPillsComponent.vue
index 7c85bfbf6..6064cc981 100644
--- a/frontend/app/src/components/Activities/ActivityBellowMPillsComponent.vue
+++ b/frontend/app/src/components/Activities/ActivityBellowMPillsComponent.vue
@@ -145,6 +145,9 @@
         :datalabelsFormatter="
           (value, context) => {
             const timeSeconds = getHrBarChartData(hrZones, t).timeSeconds[context.dataIndex]
+            if (!timeSeconds || timeSeconds === 0) {
+              return `${Math.round(value)}%`
+            }
             const hours = Math.floor(timeSeconds / 3600)
             const minutes = Math.floor((timeSeconds % 3600) / 60)
             const timeStr = hours > 0 ? `${hours}h ${minutes}m` : `${minutes}m`
diff --git a/frontend/app/src/components/Activities/ActivityMandAbovePillsComponent.vue b/frontend/app/src/components/Activities/ActivityMandAbovePillsComponent.vue
index 26d57c8e4..3aee0d06a 100644
--- a/frontend/app/src/components/Activities/ActivityMandAbovePillsComponent.vue
+++ b/frontend/app/src/components/Activities/ActivityMandAbovePillsComponent.vue
@@ -127,6 +127,9 @@
               :datalabelsFormatter="
                 (value, context) => {
                   const timeSeconds = getHrBarChartData(hrZones, t).timeSeconds[context.dataIndex]
+                  if (!timeSeconds || timeSeconds === 0) {
+                    return `${Math.round(value)}%`
+                  }
                   const hours = Math.floor(timeSeconds / 3600)
                   const minutes = Math.floor((timeSeconds % 3600) / 60)
                   const timeStr = hours > 0 ? `${hours}h ${minutes}m` : `${minutes}m`