I received some information about the procedure at Galaxy Con if you booked a chat with TJ. A friend just had a chat with an actress on there.
The Team seems to be all professional. Before you get to chat with TJ, a tech person from the staff will test the technical seetings of your camera and microphone with you to make sure that you won´t face any surprising issues. After that you´ll be send to a waiting line with a counter on which you can see your approximately waiting time until it is your turn.
During your chat with TJ you will see the time you have left. At 30 seconds the deadline is highlighted but the Star has the opportunity to "snooze" it, which would mean additional 30 seconds for you. (It might depend on how many people are in the waiting line if they do or don´t do). I don´t now how often this procedure is possible. My friend told about two times the actress she chattet with hit snooze.
After you´re finished the video of your chat will be available online latest after 24/48 hours. The participants lately told about an availability after two hours. No guarantee here that it will always be this fast.
I hope this information will help you a bit planning in advance.