What to do if I want to have a full-time job while still studying

I recently got a good job offer. With good salary, nice collegues, reasonable boss, etc. Only one problem: it's a full-time job, and I don't have a flexible time table. So my next semester will include me constantly being late to class and doing really bad with all my assignments. I have to ask: should I hire someone for the sake of them doing my assignments? Maybe a writing service, or something like that.