The 2 in soi Hotmail are likely the best bet-for time only, not necessarily for quality. reportedly there are now 2 on soi 4/Silom, but this soi mostly also closes sharp at 2.00.
See on travelgayasia.com or the recent new blog from div.madman (bkkmassages.wordpress) for listings-most advertise they close by 22/23-thats 'last orders''. Some say they open 24 hrs (mostly becse they have several boys sleeping in the house)-this will likely only mean someone has to be woken up by that time.