I went on the 2016 Italy ABD. I think we had around 90 minutes of on your own time after they brought us into Orvieto, but I don’t remember exactly. The trip has changed since then. Our group had lunch after leaving Orvieto, at some villa along the way toward Florence. The itinerary now seems to hold lunch in Orvieto.
There was enough time to see the church, do some shopping, and get the gelato that the guides provided. I also walked to one edge of town to get some pictures of the surrounding area.