What is the number in log file names of elastic beanstalk on s3 means?

I set to save log files of my elastic beanstalk on S3 through Cloudwatch. As I checked the saved log files, some numbers come after "access.log" but don't know what it means. Is there any way to set log file name as {saved-time}-access.log? Or can I know what this number means so that I can schedule a daily job parsing the day's log file?