I have a prospective new job, I'll be finding out in the next few days if I get to be a part-time courier at a law firm. I am wondering when to ask about accommodations, what counts as an accommodation, and if they can refuse me the job because of accommodations?

Namely, I very occasionally unexpectedly need time off because of my mental state, and I need to not be punished for taking of days for self-care when it is vital. This is the accommodation I'm looking for. I recently signed up and was approved for Workability thru the dept of rehab, and they're supposed to be helping me, but I've been unable to get them to schedule an appointment with me which is crazy frustrating.