You can always have two active bookings at a time and one active booking per day. As soon as you have attended one of the events, you can book a new one!
You can of course cancel a booking if you find another event you rather wish to book (cancel is always free of charge if it's more than 24h before the events takes place).
The number of bookings on standby is unlimited, but please note that you might have to cancel a booking in order to accept a reservation in standby.