I'm sort of in the same boat! I applied to 6 schools, 4 have gotten back, 2 I am seriously considering. However, one of them has an acceptance deadline for April 30th, the other for April 2nd. Of course the admissions gods decide that my top choice schools respond the latest - and I have no idea when they will release decisions.
I sent an email to the admissions department for both schools to extend the deadline until May. neither have gotten back to me. I hope it doesnt end in a rescinded offer...
anyways, it depends how ok you'd be to settle for this 2nd school, like if you didnt get in would you really be happy going to this 2nd school? in that case id drop the $600. presuming your first choice is a reach and youre not so confident you'll get it. if you are though and it's a matter of 6 days. I'd wait!
Hm, I would say no (my undergrad had students apply for housing in February, before they knew if they were admitted or not just because space was so limited) but the 23 January thing seems like a good sign! It could be that you have been recommended for admission by your department and it has to now clear through the graduate school. That's a common next step. If you really want to you could probably contact your department. Tell them you want to fill out the housing form, but you haven't received a formal offer. Maybe they'll be nice enough to clue you in.