Shift Differentials

I understand if you work 12 hours, you get the base pay for the first 8 hours & time & a half for the last 4 hours....but what about the shift differential?

Say your night shift differential is $5....is it $5 for the whole 12 hours or is it only for the first 8 hours & then $7.50 for the next 4 hours?! I thought it was first one but read something different on an old thread.

Anyone??

I have never gotten OT for going over 8hrs (wouldn't really be cost effective for hospitals these days when there is more and more of a push for nurses to work 12's). I have however, gotten a 20% differential to work nights, and a 10-15% differential to do Fri evenings and weekend daylight shifts.