format time into military format

Hi,
I'm helping one non profit with they donation pickups, they getting some pickup schedule and need to sort it and put time into military format, eg.
2:30pm --> 14:30
And it doesn't work for me, I do Format Cell > time > 13:30 but my "2:45pm" stays as is, is it possible to accomplish, ideally with macro. I also tried to do Format > Protection > Unlock those columns, but still no result.
Original list composed by diff people so we can't rely on any standard, so I try to take existing file and apply formatting in one place before processing.

Appreciate your help, Excell is really tricky for some users, I'm using either 2007 or 2010.


Best
Dai