You can hide a class/tour/game/event/workshop on a specific date and time from your booking page, and set that only customers with a specific link can make bookings for it.
1. Go to your Calendar
2. Click on the class/tour/game/event/workshop on the specific date and time
3. Go to the Access tab
4. Tick the Hidden [1] checkbox
5. Right-click with your mouse on the link, select Copy link address
6. Click on the Save button
7. Give the copied link to your customer(s).
The secret link will not work if you only allow bookings from members - whether you have set that the class/tour/game/event/workshop can only be booked by members, or if all bookings are restricted to members only.
Click here for more information on memberships.