I work 3 side jobs while in first year, I get mostly A's and B's (more B's than A's) and have a wife and duaghter. It means I don't spend much time with friends though most people at school like me. There are a few other students doing research positions both at our school and outside it.
Mostly it depends on what you want to spend your free time on and how quickly you pick up on the material.
If you are single and plan on dating and having relationship drama, don't plan on it. If you family is high maintence, don't plan on it. If you live far from campus and have to spend a couple hours a day in transit, forget it. I wouldn't go into school with work, but see what your schedule looks like after the first month and then decide.