Reservation expiration has couple of settings:

Online payment only
After reservation
Before booking
Disabled

And what is the difference between pre-reserved and reserved

What are the difference i set for example online payment with bank transfer and the system adds a 20 minutes for expiration ? what are the rest responsible for?

Hello,

we are preparing new documentation and I think these things will be described there.
For now:
1. Disabled is functionality as before. Customer book reservation. It is newly in status pre-reserved (not approved by administrator). But pre-reserved status block also selected time units.
2. Online Payment Only works different way. It allow customer to select only specified payment methods. Those which are made to pay immediately. New order has status Canceled. It will not block selected time units and other customers can still book them. But after payment, Book it! modify order status to reserved. It will block selected time units and other customers will be not able to book them (if there is no more capacity for them). When 2 customers will book same time unit at the same time, it will be booked by that customer who will pay sooner. Second order will be automatically set to status conflicted.
3. After reservation and Before booking are similar to Disabled. But if you set that order has to be paid 2 hours after reservation, then if it will be not paid until that time, plugin should automatically change status of order to Canceled. Same with Before booking, but there is important another time. Order has to be paid specified number of hours before selected time.