They have to be offset by one day.  Out on Day X, and in on Day X + 1.

With manufactured parts I know the Phase In/Phase Out dates can be the same date.

Example:

Transfer revision 1 today with phase in date of today, set it buildable, then transfer revision 2 tomorrow with phase in date of tomorrow. Phase Out date of revision 1 will be the same as its Phase In date.

Thanks @matt.watters 

I misread the question not realizing it was meant to be within the same revision.  Agree with that answer.