Overtime calculated correctly with this method, but "0" showed up in regular
and nights and weekend. I don't have space for blank cells to be underneath
B4:M4, because all of the workers are listed top to bottom, and there can't
be any gaps between them.

Just to help you understand the look of the cell better:

B2 says "SAT", C2 says "SUN" and so on through the days of the week. N2,
O2, and P2 say Regular, IPR (which is our abbreviation for Nights and
Weekend), and Overtime, respectively. Then, in B4 we put in Saturday's
hours, C5 is Sundays, and so on all the way across to M4. Each Day of the
Week has a day cell, and a night cell. For example, Monday regular is D4,
and Monday night is E4. So, I have it all broken out as it should be. I
just need IPR and Regular to stop calculating once they combine to hit 40
hours, and Overtime to pick up all of the hours over 40.

But, I can't have blank cells in row 5, because that is the next guy's
weekly hours.

Thanks so much for your help, hopefully this makes sense.