Going through the same process myself and was also curious about the timeline. From what I've heard it's approx 45 days, give or take, from signing the concurrence.
I could be wrong, but I'm under the impression that all leave has to be sold back up to the certain point. I believe any amount over 60 days that has been sold can stil be used as leave. So if you've already sold 60 days of leave, you may still get to take Terminal leave or whatever it called.
If you don't have alot of leave, I'm under the impression that they'll want/require you to sell it back before establishing your DOS. This is just in my opinion based on my limited knowledge of the process. It may be different in your case but I just thought I would bring that point up.
Please get confirmation on this before making a decision based on it. I could be wrong, but I just wanted to bring up the point of leave being sold back to aide in the answer of your question