I'm at Keesler right now. I'm in ICU, so our schedule changes about 6 times after the original schedule is put out due to deployment taskings, tdy's, sick calls, etc. We just had 2 civilian nurses have to take 2 weeks off because we had too many civilian hours, so of course the military nurses had to be moved around to cover. Then you have meetings, sometimes with notice, other times no notice. Then there's nurse calls, commanders calls, change of command or promotion ceremonies. The schedulers really try to keep the schedule from changing, but it's almost impossible. The only way to guarantee certain days off is to take leave.
The med/surg floors don't get tasked for deployments as frequently. I think their schedule stays more consistent than ours, but they're still required to attend meetings, nurse calls, commanders calls,... I actually talked to someone last night from the medical floor that had gotten called in for a night shift because someone called in sick. She only had enough notice to take a few hour nap before going in.
I guess the best thing to do is plan for the worst. If you work, plan to be the primary parent to pick up the kids and be home during holidays. He'll be able to help out, but his schedule will definitely be unpredictable. And when they call him to come in, he's going in. The good thing is when they're able, the commanders try to make up for those extra days worked. Unfortunately, family members of active duty make sacrifices too! I couldn't have done this without a very supportive husband!