It appears like the estimated time for dungeon group finder just randomly picks times (set times it seems) to show.
This is what mine looked like every few mins (after over an hour await)

I think what would make it better is just show your place in the queue. Like "Your are 89th in queue". Then you can at least see the number go down to show progress. It does this when you try to get into a full campaign in Cyrodiil.