Reinstalling macOS High Sierra from Recovery Tools takes many hours on 2016/2017 MacBook Pros
The one thing that I would say is that Apple has changed the recovery process somewhat in 10.13 High Sierra. Newer model Mac computers now have to pull down much more from Apple's side. 

What sort of internet connection are you on. 5 - 6 hours does sound pretty extreme but 2 - 3 hours I have seen in our lab at work for sure!