Firstly, I'll assume you plan on doing quality study during the hours you would be working, if you decide not to get a job.
I reckon it depends on your study habits (do you study consistantly? or do you bludge till the last minute and not do as well as you could have? are you better at putting in quality, or quantity?) Can you do really well without putting a lot of effort/time in?
I think having a job, even for a few hours a week, looks good on your CV later (shows you can balance school/work/leisure - nobody has to know -exactly- how many hours you worked!) and it gives you a balance.
You gotta remember... some people will spend the same amount of time you spend working at the beach, out partying, playing sport or just doing nothing. At least you'd be getting money and experience
So I say go for it, you can always quit later if you find you need more time for study.
Also, depending on the job, you can sometimes put in study while you work... I sometimes learn new german vocab while I'm cleaning or just think back to what we learned that day while vaccuuming. [/geek]
Anywho... what UAI/uni course are you aiming for?