Several girls I work with have other things going on other than working.
Would this be a freelance or a permanent position?
As far as permanent positions go, there are 15, 18, 20, 24 & 30 hour a week positions. My understanding is that when they give you your position you are guarenteed at least that many hours a week.
I have worked in both a freestanding and a counter. As far as they both go, daily shifts are 6-8 hours, depending on the day (somtimes more, during holiday & extra busy times). A 15 hour is split between Saturday & Sunday & 18 hours is usually Friday, Saturday & Sunday...these two are usually the best for students. I don't know about the other shifts, since at the time it was explained to me, I was a student & that was all that mattered.
Best of luck to you...and Happy Birthday!