IMO - Bit should be washed and dried after every use. Leather cleaned minimum weekly, more often if wet & muddy. If used a lot oiled twice per year. I think staff/helpers should do it.
I used to work at a riding school when I was younger, tack got cleaned saturday lunchtime and afternoon after the main rides were through. The main trade was on a thursday and saturday. Tack was cleaned by us (slaves) helpers and checked by instructor.
Last place I worked did lessons- our tack was cleaned twice a week ish (or more if we felt like getting out of the bosses way!) Bits were never rinsed after each ride though. Why do you ask?
EVERYWHERE I have ever worked tack cleaning was the last job of the day, EVERY day and basically it was a case of "If it's been near a horse clean it" memories of sitting in cold, clammy tackrooms, frozen to the core, tired, miserable and peckish at the end of a day cleaning strips of leather is not one of my fondest. Which is why for the last 15 years or so my everyday exercise tack has been minimal and synthetic. Ugh........I can TASTE saddle soap (always bars not spray)
In answer to the question though I'd want it cleaned and checked properly at least once a week. If I ever ride anywhere, apart from the horse naturally, the tack is one of first and lasting impressions of a set up I have.
IMO it should be cleaned regularly for both the horses comfort and everybodys safety, fine having it cleaned by helpers but ought to be regularly checked by management/staff to ensure stitching etc is in good order.