Days with Rotation Community Living Cntr Department of Veterans Affairs

I’ve been going through the whole onboarding process and got my final offer as a practical nurse with the Community living centerThe original posting said for the schedule it would be days with rotation. They’re telling me it rotating weekends, which I’m fine with. Further, it says I may get rotated to another shift like evenings and nights. My interview for the position never mentioned rotating to other shifts. I reached out to reach hr and they only stated “ The union contract requires that nursing staff will rotate fairly and equitably.” Anyone in a similar role as mine have to rotate shifts? How long and often does occur? Apparently, the supervisor is on vacation all of this and next week. Any suggestions?