Depending on several factors (kids, wife, how tired I am, etc), 2 to 3.5 hours per night, after the kids are asleep.
The sucky thing is the next morning...but I've found I do a lot better on 4-5 hours of post-modeling sleep than I do on 8 if I skip the bench. That decompression time leads to MUCH better rest in quality, if not quantity.