If there are no available performance times available for you to schedule your event participation, it means that the event in question is already is fully booked. Please note that performance times are limited and are available on a first-come basis: you need to be the first Artist to schedule a slot to grab it. Try to sign up for a performance time as soon as possible to ensure the best performance times!
Note that even if you did not manage to book a time, since other Artists might cancel their participation, you're advised to keep checking the event schedule for any openings. The event will always display the current available performance times in real-time.