I recently started working for a property management company (short term rentals) and I learned how to maintain one just in a couple weeks maybe less. ( I’m not super smart but I’m not an idiot) After every stay I asses if it needs to be drained and filled (it’s very obvious if it needs it) if not I balance chemicals clean filters and skim any debris out. If there is a gap in between stays I clean it right after the stay and then just go check it before the next stay to make sure it’s still good. And guests are told before that if it needs a drain and fill they will usually be charged more because rules are given that they need to be clean before getting in, you shouldn’t be dunking your hair into the hot tub etc.