Amazon Cloudwatch service not returning metrics information of EC2 service

I am writing a java code for retrieving Amazon EC2 metrics using Amazon Cloudwatch. Below is the code:

        AWSCredentials awsCredentials =  new BasicAWSCredentials(aws_accessKey, aws_secretKey);
        AmazonCloudWatchClient cloudWatch = new AmazonCloudWatchClient(awsCredentials);

        Dimension instanceDimension = new Dimension();
        instanceDimension.setName("InstanceId");
        instanceDimension.setValue("i-480de11e");


        GetMetricStatisticsRequest request = new GetMetricStatisticsRequest();
        request.setNamespace("AWS/EC2");
        request.setPeriod(60 * 5);

        ArrayList<String> stats = new ArrayList<String>();
        stats.add("Average");
        request.setStatistics(stats);

        ArrayList<Dimension> dimensions = new ArrayList<Dimension>();
        dimensions.add(instanceDimension);
        request.setDimensions(dimensions);
        request.setMetricName("CPUUtilization");

        SimpleDateFormat format = new SimpleDateFormat("EEE MMM dd HH:mm:ss z yyyy");
        Calendar cal = Calendar.getInstance();
        cal.setTime(new Date());
        cal.add(Calendar.HOUR_OF_DAY, -5);
        cal.add(Calendar.MINUTE, -30);
        Date endTime = format.parse(cal.getTime().toString());     
        request.setEndTime(endTime);

        cal.add(Calendar.MINUTE, -10);
        Date startTime = format.parse(cal.getTime().toString());     
        request.setStartTime(startTime);

        GetMetricStatisticsResult getMetricStatisticsResult = cloudWatch.getMetricStatistics(request);
       System.out.println(getMetricStatisticsResult.getDatapoints().size());

The above is returning zero though I can see the metrics data in AWS console. Few thing I would like to clarify:

1) Do I need to set endpoint like cloudWatch.setEndpoint(....)?

2) Could there be an issue with setting start/end time related to format etc?

Any help will be appreciated.