Question About hold downs

Okay so my husband was offered (yes, they actually called and offered) a hold down and he accepted it. His "day off" is tomorrow and it's on the schedule as n/s for that day. I know that technically he's not guaranteed that day off because they can put him on another route (at least according to what I've read on Federal Soup) but if the schedule says n/s and no one told him that he needs to come in tomorrow, is it safe to assume he has tomorrow off? If they call and try to get him to come in, would it be okay to just ignore the calls? He's well past his probation if that helps.

Normally he would want the hours but his step-mom is in the hospital and he was wanting to visit her tomorrow.