They did have tiered seating. Rich and powerful down by the action, poor people up top. The emperor, vestals and senators even had their own entrance.

There was assigned seating, unless I don't understand the meaning of the phrase. Each gate had a number, each section had a number and each seat had a number. (Donovan. Rome, Ancient and Modern: And Its Environs, Volume 4). Ticket-taker people were stationed around just as they are baseball stadiums today to make sure people were going to the right place.

The tickets were also 'free,' in that the organizers gave them to people without taking payment in return. People probably "paid" for good tickets somehow, but it was informal. How the tickets were distributed isn't totally clear, but it seems likely that the emperor (or organizer) gave bulk tickets out to a select number of high officials, who parceled them out to their underlings, who parceled them further to their underlings and so on, down to the commoner. (Ward, Heichelheim and Yeo).

Imagine your boss gave you tickets to a football game and you go. Other than what you were watching (more head trauma, fewer stabbings) the experience was essentially the same in Rome.

Cuneus = Section (well, "wedge") Gradus = Row Locus = Seat

How often did events get hosted there?

It was profession based. With the profession came a certain class and you were put in different sections. The higher class were basically court side, then the middle class who were a little higher up and farther back and then the lower class and poor people were at the very top. For the middle and lower class it was first come first serve as there was only a limited number of seats. The higher class were usually senators or magistrates so they had a specific seat which would have been labeled with their name. Some of those named seats remained and you can see them if you go on a guided tour of the Colosseum. The middle class had it's own section and with that there were subsections for each profession.

With that separation of class came the actually ticketing and gates. There are numerous number of gates that would have been labeled and you would basically had a piece of poetry that had a gate on it. The higher class did not need these as they had their on seats labeled. The middle class did because if they went to the wrong gate they would have been in the wrong profession section.

What time of day did the events take place?