If you are running beta 13, you don't need to worry about it, the bug has been fixed.

A Jiffy is a clock cycle, it's part of the timer mechanism on computers. Sometimes software is dependent upon these timer mechanisms. A small bug in the 2.0 beta 11 software related to this would sometimes cause the user interface (your button presses) to stop responding for a period of about 20 minutes.

This bug was fixed in beta 13. It was also fixed in the Hijack kernel.