how do I change a cell permanently to PM from AM?

I would like to do this permanently to the template, so that I have
timesheets that I don't hav eto change everytime I input my time data. Thx

The question is not clear so here are some suggestions

B1: =A1-0.5
A1: 11:00 PM ---> B1: 11:00 AM

=IF(A1>0.5,A1-0.5,A1)

Menu:Data>Validation... Allow:Time, Data:Less then or Equal to, End time: 12:00


Hope it helped
Ola Sandström