They will "cut" your hair on Day 2 no matter what, but my advice is to get it cut beforehand. I cut mine really short a few weeks before so I could get used to it. They barely touched it at the OCS barber shop (although they touched it enough to make it uneven and ugly).
OCS regs are that you're not supposed to have more than 3 inches of hair. After the initial haircut, you can sort of get away with not cutting it, depending on your particular hair. If it grows slowly, if you can hide the length well, etc. Just keep it really neat or you will be sent to the barber shop.
It is so hot down there that you'll be glad to have short hair anyway. And every other girl has short hair, too, so you won't really stand out or anything.
I got mine "fixed" on a weekend at a real hair salon because the OCS barbers really suck!!