When we bought, we had to send in a deposit within days of the offer. I believe it was 10%. Then, when we passed ROFR and got the closing documents, we had to send the balance in with the final paperwork.
Depending on how long ROFR takes (it can take up to 30 days), closing might not happen for 6 - 8 weeks.
In my case, it only took 4 weeks, but that was in 2009 and they were taking only about 2 weeks to decide on ROFR.
Good luck!