How it works in reality: If you cross the average wait time by 2 minutes, it moves the AWT up until it hits 30 minutes, and then it just stays there. You can be in that queue for 2 hours, at that point I believe it just drops everyone.
How it works speculatively: If no needs are listed, the queue is empty. Whichever "need" listed is what the queue needs most, so in theory whatever "need" is listed should have an instant queue, but that also means that you could still be waiting since you need 2 DPS for 4-man content, and at least 4 for 8-player content and 24-player content.
In practice, the PvP queues are dead, and are always dead because of bots.