Average wait time: Less than 5m.

[LilimoLimomo]

So why does the game tell me it'll take me less than 5 minutes to find a group to do an activity, yet it takes more than 8 hours to find that group?

I believe this is the core issue: you have misinterpreted what "Average Wait Time: Less than 5 minutes" means. It does not mean "you will have a group in less than 5 minutes."

Because there's nothing that the devs can do to tell you how long you will be in the queue. To do that they would have to predict the future. Specifically, they'd have to know how many people would join the queue, and when, and whether they would abandon or not, etc. There's simply no way to know this.

So they try to give you the next best thing: the average wait time. But remember, the average wait time is not an estimate of how long your queue will take. If when you join the queue there's only 1 other person queued, and they've been waiting for 4 minutes, then that means the average wait time is less than 5 minutes. I hope you can see why that in no way indicates that you'll get into a game promptly. And that's why over time as you stay in that queue without getting a game, the average wait time will generally increase, because your wait time is a meaningful part of that average.