I worked just under full time and it was still exhausting because I was being over worked which made me depressed
Both. There is a cherry-pick of hours, usually they go by season, and you will pick the shifts you're able to work for according to the season, prompted by seniority of staff. This will be your fixed hours, unless otherwise stated. But, if you need a day off or can't come in the next couple of shifts then, if you're unionized, it's fine -- I can't speak for non-unionized stores.