No cut off time but the house girls tend to slow down from about 9pm, and many of them are finished by 10pm to 11pm.
Ive seen guys arriving as late as 11pm for the last hour or so and getting nothing. I think alot of people are under the impression that the Thursday party goes on till about 2 am. It actually finishes at 12am but can linger on till about 12.45am.
Can be a bit slow to get going, house girls often dont start till near 3pm, and the actual swinger women and couples tend to really get going from around 6pm.