I currently work at a startup and am doing grad school for my masters in pattern recognition. The way the grad classes are designed, you should be able to work and go to school at the same time, because pretty much everyone in your class is working currently too (whether it be 30 hrs a week in research or, say, 40 a week at Garmin). The classes are lecture heavy and the homework load is way lighter than undergrad (tougher, yes, but nothing you couldn't finish in a weekend).
tl;dr try and do both if possible, cus it'll only suck for 1 year