On the ticket it says to get there 15 min ahead of time. When we got there, we realized why this was the case. It was excellent! Booking through coop culture was the more challenging part. The Wonders of the Colosseum: Visiting the Underground and Arena Didactic from Coop Culture looks like it will get them what they want.
My son and DIL would like to see the floor/underground of the Colosseum, but with limited time in Rome that day, they want to spend an hour +/- before going over to The Forum. Our family will be in Rome on Tuesday, September 13.