change alteration period to 30 minutes when generating summary message

cat-home/src/main/java/com/dianping/cat/report/task/alert/summary/AlertSummaryExecutor.java

@@ -32,6 +32,8 @@ public class AlertSummaryExecutor {
 
 	public static final long SUMMARY_DURATION = 5 * 60 * 1000L;
 
+	public static final long ALTERATION_DURATION = 30 * 60 * 1000L;
+
 	private List<String> builderReceivers(String str) {
 		List<String> result = new ArrayList<String>();
 

cat-home/src/main/java/com/dianping/cat/report/task/alert/summary/AlterationSummaryContentGenerator.java

@@ -42,7 +42,7 @@ public class AlterationSummaryContentGenerator extends SummaryContentGenerator {
 	}
 
 	private Date getStartDate(Date date) {
-		return new Date(date.getTime() - AlertSummaryExecutor.SUMMARY_DURATION);
+		return new Date(date.getTime() - AlertSummaryExecutor.ALTERATION_DURATION);
 	}
 
 	@Override