Average wait time: Less than 5m.

[Hasrat]

OK!

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'd say here lies your own misinterpretation.

The system isn't telling you how long you will wait to find a group.

The system is telling you how long you will wait in queue. There's no guarantee it will find a group.