Timestamp extension is added to every file in HDFS sink. For a matter, it is added to every sink using BucketWriter.java. Line 247 -249 adds this timestamp counter to filename and it cannot be configured in opposite to what Ambud Sharma said in parent task.
Event creation time is not necessary a time of event saving into hdfs, obviously events can be delayed. Thus I don't know why file creation timestamp is mandatory - it can be confusing.