Most people I've heard pass ROFR some time in the last (4th) week. The low-down is that they make their decisions on a Monday/Tuesday, so you hear then. So depending on which day you submit your contract, expect to hear about the Monday/Tuesday before your 30 days end (so mid-20s).
If your contract does not pass, it could be faster. I haven't heard a lot of data points about ROFR'd contract notification time.