I was just in HK 2 days ago but came in a group. I found there are a few 24-hr places so I can slip in at 3am.
I was staying in TST so I tried out contacted Serenity Spa (
https://hongkonghappytantricmassagehk.com/) and confirmed they are 24-hr and asked for pics of available WG. It's massage + happy ending, but better than nothing.
I just filtered through the database with 24-hr option, but make sure you message to double check.
Best ouf luck!