We usually change the bedding weekly, I.e. every Sunday and the towels usually as soon as they start to develop this old wet umbrella stench, which takes about 3-4 days.
Oh my god, that smell is mildew. If your towels are kept so humid that they’re mildewing the colliform bacteria in your bathroom is having an entire festival on there. Please, before you get a horrible infection, please start swapping them out more frequently. I’m begging you, rubbing that on even a small open wound could be legitimately life threatening (for example if you’re the lucky winner of E.Coli roulette, which is also absolutely growing on your towels).