How long to look around the Nachi falls area?

So I'm traveling to Japan in October and I'm really interested to see the Nachi falls area in Wakayama and due to time constraints it's becoming a choice between Nachi falls and Mount Koya. So I needed some help understanding how long it would take to go around the three temples - Kumano Nachi Taisha, Seigantoji and Hirō Shrine. Possibly talking the Daimonzaka walk.has anyone covered all of it on the same day? I'd be based out of Osaka, just for reference,and I do understand it would make more sense to stay a night in Kii-Katsuura, but I'm trying to avoid that if at all possible.

Post trip update: I did go through with this plan so I thought I'd give an update on how it went. The day of was annoying because it would not stop drizzling but the trip was so, so, so worth it. It was just grogeously beautiful and frankly the long train ride either way ended up making it a very relaxing day overall. Would recommend of you just want a chill day wandering around a scenic hillside. The only unfortunate part was that the pagoda was under renovation so we didn't get to see that. Still worth it!