Once an old master (Shi-Fu) told me in the old days (pre-1950's) 1 hour stands for 1 part of massage. It turns out each masseuse needs a 15 minute rest time otherwise they won't be able to move on for the rest of the day - that's why we got the 45 minute per part (60 minutes less 15 minutes).

Ironically it turns out that the masseuse won't give up that 15 minute break - rather than wasting that 15 minutes each masseuse / shi-fu would arrange it in typical Chinese enterprising manner - complete the 45 minute session and move on to the next 45 minute session.

This standard also holds true for the female only sauna where its purely veggie in HK nowadays.

Full service sauna became popularised in HK around the 1970's - at about the same time when the female masseuse were becomming a standard - Esp the opening of Ka Lai Wah whose aim was not into the technical competent masseuse; rather they prefer to have retired night club girls who are used to provide FS to their late-night club clients anyway. The difference was having FS in a sauna or in a cheap motel room. I suspect building on the 45 minute concept, the special category masseuse needs another 10 minutes for washing and bathing - before and after. (35 minute = 60 minute - 15 minute rest time - 10 minute bath and wash time) Henceforth the 35 minute for each part. I also suspect this is borrowed / mixed standard from the Night Club  where they have 35 minute standard.

Sometimes we expats felt cheated when an "hourly fee" would be paid for only 35 minutes and we screamed at the front desk - the more you learn the better you understand and avoid the conflicts with these establishment.

Say a 45 minute massage at a veggie on average fee = $250 + $100 tips / 45 minutes = $350/45 minutes = $7.7 / minute
At a FS sauna on average 2 parts = $400 + $300 for extra / 70 minutes = $10./minute

Of course again it depends on your need that night - e.g. horny for a shag or being tired plus the level and sophisication of service ... there's no price tag on a good satisafacory experience.