diff --git a/src/org/ntlab/deltaViewer/CollaborationObjectCallGraph.java b/src/org/ntlab/deltaViewer/CollaborationObjectCallGraph.java
index fff5242..6f3a808 100644
--- a/src/org/ntlab/deltaViewer/CollaborationObjectCallGraph.java
+++ b/src/org/ntlab/deltaViewer/CollaborationObjectCallGraph.java
@@ -7,11 +7,14 @@
 import java.util.Map;
 import java.util.Map.Entry;
 import java.util.Set;
+import java.util.SortedSet;
+import java.util.TreeSet;
 import java.util.stream.Collectors;
 
 import org.ntlab.deltaExtractor.ExtractedStructure;
 import org.ntlab.trace.MethodExecution;
 import org.ntlab.trace.MethodInvocation;
+import org.ntlab.trace.ObjectReference;
 import org.ntlab.trace.Reference;
 import org.ntlab.trace.Statement;
 import org.ntlab.trace.TracePoint;
@@ -25,12 +28,14 @@
 	private Set<Reference> references = new HashSet<>();
 	private List<MethodExecution> startPoints = new ArrayList<>(); // Common ancestor point
 	private List<TracePoint> relatedPoints = new ArrayList<>();
+	private SortedSet<Long> timeStamps = new TreeSet<>();		// List of time stamps of related points
 
 	public CollaborationObjectCallGraph(ExtractedStructure e) {
 		references.addAll(e.getDelta().getSrcSide());
 		references.addAll(e.getDelta().getDstSide());
 		startPoints.add(e.getCoordinator());
 		relatedPoints.add(e.getRelatedTracePoint().duplicate());
+		timeStamps.add(getTimeStampOfRelatedPoint(e.getRelatedTracePoint(), e));
 	}
 
 	@Override
@@ -53,6 +58,11 @@
 		return null;
 	}
 
+	@Override
+	public SortedSet<Long> getTimeStamps() {
+		return timeStamps;
+	}
+	
 	/**
 	 * Merge ExtractedStructure not to overlap reference.
 	 * 
@@ -117,10 +127,12 @@
 		startPoints.clear();
 		startPoints.add(lca);
 
-		// Is it in time stamp order?
 		TracePoint otherRelatedTp = e.getRelatedTracePoint().duplicate();
-		relatedPoints.add(otherRelatedTp);
-		relatedPoints = sortTracePointByTimeStamp(relatedPoints);
+		long rpTimeStamp = getTimeStampOfRelatedPoint(otherRelatedTp, e);
+		int idx = timeStamps.headSet(rpTimeStamp).size();
+		relatedPoints.add(idx, otherRelatedTp);
+		timeStamps.add(rpTimeStamp);
+//		relatedPoints = sortTracePointByTimeStamp(relatedPoints);
 	}
 
 	/**
@@ -147,6 +159,23 @@
 		}
 		return qTmp;
 	}
+	
+	private Long getTimeStampOfRelatedPoint(TracePoint relatedTracePoint, ExtractedStructure e) {
+		ObjectReference targetObj = null;
+		if (e.getDelta().getDstSide().size() > 0) {
+			targetObj = e.getDelta().getDstSide().get(0).getDstObject();
+		} else {
+			targetObj = new ObjectReference(e.getCoordinator().getThisObjId(), e.getCoordinator().getThisClassName());
+		}
+		if (relatedTracePoint.isMethodEntry() && relatedTracePoint.getMethodExecution().getArguments().contains(targetObj)) {
+			return relatedTracePoint.getMethodExecution().getEntryTime();
+		}
+		if (relatedTracePoint.getStatement() instanceof MethodInvocation) {
+			return ((MethodInvocation) relatedTracePoint.getStatement()).getCalledMethodExecution().getExitTime();
+		} else {
+			return relatedTracePoint.getStatement().getTimeStamp();
+		}
+	}
 
 	/**
 	 * Sort TracePoint in time stamp order.