Two places that advertise quite openly online that they have 24 hour outcall service are:

Moon Boy Massage ( which is in fact the nighttime name of Baan Tewa, my favorite one ), 080-249-6336 or 02-679-0816

J Club ( I'm trying today for the first time ), 087-908-4543

I have the managers of Baan Tewa, and The Prince, and Water Nest, and now J Club, on my LINE chat..... So sometimes I can chat with them directly, even if it's at 3am or 8am... ;-)

By the way, some of the places I would *not* recommend include: the Tawan Massage ( now called Sun Massage ), and pretty much *all* of massage shops along Silom near the BTS station. In my experience, all of those are the same. Lousy massage, badgering you with "How much you tip me?" questions the entire time, followed by lousy extra service. So not worth it. So only for naive tourists.