From my experience (and I'm still very new) this depends on a ton of different factors. I'm AF and working inpatient so my shifts are rotating 12s (days/nights). The floor I'm on tries to do 3mo rotations of days/nights but it doesn't always work out that way. There really isn't a set number or days on/off...varies a lot but the they try not to schedule for more than 3 on in a row...again that varies. Some of the nurses prefer days/nights and verbalize it to the scheduler but bottom line is mission comes first and we're not self-scheduling.
Clinic nursing in the AF is different than inpatient/ICU/ER. The schedules are pretty consistent but the work is different. Hope that helps a little