Subtracting date / timestamps

I have looked through the forums and found many date / time manipulation tools, but cannot seem to find something that fits my needs for the following.

I have a log file with date time stamps like this:

Jun 21 17:21:52
Jun 21 17:24:56
Jun 21 17:27:59
Jun 21 17:31:03
Jun 21 17:34:07
Jun 21 17:37:10
Jun 21 17:40:14
Jun 21 17:43:18

I need something that "subtracts" the time from the previous entry and
displays the "minutes:seconds" difference.

These should all be around 3 minutes apart, and I am looking for descrepencies.

Any hints on how to do this would be greatly appreciated.

Thanks.,..