At what point do you allow prospective parents to visit your setting?

So...I am 99 percent sure that I will have a space on a couple of days in September. However, three of my current mums circumstances are changing come September and might be wanting to swap/reduce/increase a day here and there. They are all speaking to their bosses currently, so everything is up in the air.

I also have a couple of prospective parents who haven't made firm plans on what days they will need (talking to their bosses too, at the moment). They are probably weighing up all of the childcare options too, which will influence what they try and negotiate with their bosses maybe. Fair enough.

Soooo, would you let people come and visit before they properly know what they want and before I properly know what is available? Or do you wait until you are both certain of what you can offer/need?