I don’t think an hour is enough free time…but everyone’s different.
If you’re really interested in nature, hiking, or even just the beauty of trees, I would advise that you go there on your own and have your own time at your leisure. If you’re just going to say “Yay, now i’ve been to Muir Woods” ...like checking it off your list…then you may be fine with the tour, however.

I really enjoyed just sitting in the woods early in the morning and kind of just being with the trees. They’re so old and tall and it was so quiet and peaceful and not like anything else in my daily life. I didn’t have time to see everything and hike everywhere, but I did enjoy what time I had. There’s alot to look at and take in and sitting still offers that in a way that trampsing around quickly can’t.

I drove up to Muir Woods twice…the drive up there is a good 20-30 minutes from the main road….I only spent about two hours there altogether….I actually skipped a whole morning of a conference to spend time there, it was so beautiful I couldn’t leave.
The benefit of getting there really early in the morning is that you can park easily and you don’t “have to” pay admission. But I still would advise leaving a donation and buying something from the gift shop/concession to help support the park.

Hope my advice is helpful. Enjoy your trip!