It's 24 hours. The services stop around that time and maybe they reached capacity? I've never been turned away and have come there random times of the day.
My friends and I have come in at 3am and we weren't turned away. There aren't any services available until after 10 AM, so most people sleep or soak/wash.
The massage and private services stop around that time, they clean and folks are sleeping. We left around 2 am but can't remember if there was anyone coming in.
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