Ive been asked to figure out how early an employee typically punches in for
work. They want to give her some sort of bonus. I have the punchclock data
in an excel column in the following format:

5/14/07 10:02 AM
5/15/07 9:16 AM
5/17/07 9:28 AM
5/18/07 9:16 AM
5/22/07 9:15 AM

Shes supposed to start work at 10:00am every day, and I need to figure out
what time she usually checks in. Ive tried a typical averaging formula, but
that gives me the mean time between all of the days, which is around noon on
the 17th.

Any ideas?