You should calculate four and a half hours. There is no cell phone reception. If something happens to you. You better not go alone. You urgently need sturdy shoes. Definitely worth seeing. Great impressions. But in any case you need a good condition because you have to climb over big rocks.
The tour is great. Climbing over the rocks was fun for everyone (youngest participant 13 years). Iron is embedded on the slightly larger rocks, so all passages are easy to overcome. It is recommended shoes that have "a bit" Gripp, as the rocks are polished some pretty smooth. We took 4 hours with breaks and a lot of photo interruptions. Marking the path is good enough, if not lush - but since it goes through the riverbed is only the entry and exit really relevant.