I don't know if the account will be frozen. In my first D, nothing was frozen, but I think that's a choice between the parties, not automatic. I suggest you take the money out now so you don't have to worry about it when you need it.
I really hope you follow my advice about custody. Don't assume she will get it until you consult a lawyer. D sucks, but if I agreed to what my exW wanted and became a weekend dad, I would have hated myself for not fighting for my D11 and I would probably be resentful of my exW to this day.
Also, if it comes to it, don't agree to a typical 80/20 agreement if you're going to actually have them more than that. If you are going to have the girls 30% or 40% or 50% of the time...put it in writing. The worst thing you can do is have the girls half of the time, but pay CS as if you didn't. You won't have a pot to piss in.
Fighting for my D11 didn't change the outcome of my M, but I think it did help earn my exW's respect and most importantly allowed me to be as big a part of my D11's life as possible. Incidentally...my exW and I have a fantastic R today.
Me45 (D11 from 1st marriage) W43 (D20 & D16 from 1st marriage) M4 Bomb 6/16/09 W wants D W moved out 8/29/09 I sent her D paperwork 9/25/09...I'm done