I agree with Virendra. Although you can use a common Data Entry profile for PS/CS it is not the best practice. Data Entry profile basically controls as to what fields you would want to be used while using the CAT2 tcode. Apart from this there are a lot of other things a Data entry profile controls.
Hope you take a good look at the Data entry profile and seggregate the requirments for timesheet entry for PS & CS. This will help you in understanding this in a much better way.