diff --git a/analysis/gc-log/src/main/java/org/eclipse/jifa/gclog/model/GCModel.java b/analysis/gc-log/src/main/java/org/eclipse/jifa/gclog/model/GCModel.java
index 0703b2ed..6a610a40 100644
--- a/analysis/gc-log/src/main/java/org/eclipse/jifa/gclog/model/GCModel.java
+++ b/analysis/gc-log/src/main/java/org/eclipse/jifa/gclog/model/GCModel.java
@@ -466,6 +466,13 @@ public void autoDecideStartEndTime() {
             endTime = Math.max(endTime, event.getPhases().get(event.getPhases().size() - 1).getEndTime());
         }
         setEndTime(Math.max(this.endTime, endTime));
+        // update start time.
+        event = gcEvents.get(0);
+        double startTime = event.getStartTime();
+        if (event.hasPhases()) {
+            startTime = Math.min(startTime, event.getPhases().get(0).getStartTime());
+        }
+        setStartTime(Math.min(this.startTime, startTime));
     }
 
     @ApiMeta("timeGraphData")