French visa from London...how far ahead is the appointment likely to be?

Hi all, I understand that slots for French visa are in high demand and limited in availability. I will soon start an application and I'm wondering how far in advance I should make my hotel/euro tunnel bookings. I'm reading here in Reddit that 20 working days for after the appointment should be expected...and that's fine...but how long should I anticipate to get the appointment from the point of application please? Also, is that visard telegram bot any good? Thanks all!