I think the numbers of hours you work is actually less important then when those hours are. For example, 20 hours a week, all scheduled from 8 a.m.-5p.m. M-F is killing me. But if I can get on at the hospital as a nurse tech and get some 7p-7a on the weekends, I think I could do 24 hours a week much easier. When do you best study? Make sure that whenever your peak brain power times are, you have several hours free. I can work much easier when I am a little tired then I can study when I am tired, so working during the week day and then coming home at night to study for quizzes, tests, doing assignments, paperwork for the next day just isn't working - I am too drained. I would MUCH rather have a few hours a day during the week to just stay on top of things, go to the lab, meet with instructors then let all my homework pile up for the weekends.
My second piece of advice is try it, but have a very clear back up plan in case it doesn't work out. Make sure you have a plan b - to take out additional loans, work different shifts, etc. It is most important that you prioritize your school work and I find that unless you already have some back up plans, struggeling to get your work hours in at expense of school can suck you in.
Good luck - while I feel constantly busy, I do not think n school is as hard as it is made out to be - yet :fingerscrossed
One last caveat - I am one of those people who can barley function on less then 7 hours of sleep. If you are one of those people who can make it by on 4-5 per night, disregard all I've posted.