New hire here. What is considered a work week at Costco?

Hi! Newbie here, FT college student working PT front end. just accepted my position! Super excited to get started!

Unfortunately, I'm also a college student and finals are right around the corner. I have no problem working 24+ hours for a usual week, but with finals it gets complicated with different times/available days/needing time to study etc. Finals last for almost 2 weeks and mine are all spread out, so I can work some days that week.

Even though I've heard that Costco is pretty good about accommodating students, I'm concerned about asking for so much time off during my probation, as I'm hoping to keep this job at least for the rest of undergrad and while I figure out what the hell I'm going to be doing after. They hired me knowing I'm a college student, but I'm then worried that all the other college kids are going to ask for the same time off (this Costco is right near a university and they say they've hired many kids from my university). I'm trying to make myself as flexible as possible to stay at 24 hours for that week, but I don't know if it's possible depending on what is considered a "week" :/

TL;DR: what is considered a "week" at Costco? Is it Sunday - Saturday? Monday - Sunday? Thanks!