Roman Colosseum release timing for tickets

We will be visiting Rome and want to purchase tickets for the Colosseum's "Full Experience Underground Levels & Arena".
I have been told that tickets for that specific tour are difficult to obtain, and they are not released until 7 days in advance.
Do any of my fellow travelers know the time of day (Central European time) that those tickets are released for purchase?
I understand that living in the U.S. may require that I get up in the middle of the night to purchase them, and that is not a problem.
Any and all suggestions are appreciated!