It really depends on what works for you. If working doesn't tax you very heavily and you can come home and get stuck into study, as long as you make yourself do so,
effectively, it's fine. It's all about time management and, urgh, goal setting.
However, there's only a certain extent of work you should do. My dad's a teacher and he's all into this kind of stuff... some study he's got showed that on average those who worked ~5 hours a week were better off in their results, leading to better levels of organisation, engery, etc. That's around your optimum workload. Anything greater than that tended to see a dip in the results of the participants.
Personally I didn't have a job, as I am a musican and we don't get jobs
, but no, it certainly took up the time commitment of one, and perhaps more effort. Try to work to at least a bit of a schedule and use your available time - read over texts or look over some summary notes during travel time... unless you're driving - I saw this P-plater reading papers while driving the other day... probably not the best idea for passing haha. Anyway, things like that seem small but really do add up over time without a much extra effort.
If you wanted to, you could get some of the easy coursework out of the way over the summer holidays which ultimately gives you more time during the year. Don't burn out though, make sure you get a decent break so you can work hard during the year.
That's my 5c.