I noticed Bigbro's comments above so will try to add some extra thoughts.
This is a general answer, there are differences between 141 walk-ups, the transient short stay Hotel girls with agents who want to have them work max hours, to the brothels in Mong Kok.
The hours posted are pretty much what they want to work, however the reality can be very different. The start times can be very optimistic, shit happens, previous long night, or overnight booking, etc. Actual availability before 1:00pm is hit/miss. That being said, if you have a hot target don't dawdle, especially with the Hotel WGs, get on the phone early.
Very rarely some WGs are particular about closing time, I suspect they may have children and/or a man to get home to. I had one girl in my hotel room and nothing would persuade her to stay past her advertised 11:00pm finish time. Most are pretty flexible, will want to work, and to get bookings (especially with reliable regulars which may work against a tourist). Once it gets around midnight they may be unavailable if they take an overnight booking.
I personally do not like hunting for chicken at 2:00am - 3:00am (unless it's in a Macau sauna), better to have girl signed, sealed and delivered well before then.
When are you in HK? Look forward to you reports.
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Last edited by Froddo at 4-12-2008 09:03 ]