Yeah I got a job in October of my second year. I work 9 till 5 on Saturdays. I was really worried about my time management, but then I remembered, I never do work on Saturdays anyway! I have loads of essays due in atm, but can confidently say that even if I didn't have a job, I don't work on weekends. So far so good. Maybe in third year it will effect me more but I guess you just have to work around it, it's only one day, and it's really helped financially.
I know people who work various shifts throughout the week at supermarkets at what not; I think that would effect me more. I prefer just doing it all in one day. I get asked for overtime a lot but I can hardly ever do it. I'm sure they understand though.