You are reading too much into the average time. It's more of an estimated time. Even then, nothing can guarantee that you will meet that estimated time. It's not like your queue is time dependant. Your queue is player dependant. If you need 1 more player from TA to complete the queue, the system would probably show 5 mins estimated. However, if no player from TA chooses to queue for the next 3 hours, you aren't going to get any queue.

The "average" time they show is just a rough estimate based on how many slots are yet to be filled. However, it is definitely not accurate as no one can predict who is going to queue and when they choose to do so.

It's not broken. That's how it's meant to be. You just read too much into the words "average", when no mathematical formula or computer code can accurately predict who is going to queue and when they will decide to do so.