How do tickets work?

The tickets are good once per summon session. Once you spend a ticket, you get the first unit free.

there's no point in saving them, no. the tickets are given for a certain banner, in this case hero fest. once hero fest expires the tickets will too. you might as well use them unless you don't mind totally wasting free first summons.

They can only be used for your first summon on the banner they’re used for (Hero Fest). Once you use one and summon you have to go back and restart another summoning pool to use another one, you can’t use them all in the same circle.