Yes it's only when they go on tour. They have plenty of time. That's the great thing about being rich, the money makes you free to do what you want when you want. It's not like, sorry honey, I can't go, I have to work! They do stuff when they have spare time but I don't think they ever let it take the place of the happier things in life. When Bono tours, they can pick up and go.
I love the quote Bono made in the Elevation program, something about travel being a better education that sitting in a classroom, that he got his education out the windows of buses and planes and from the world. So I'm sure he thinks that the traveling they do on the tour and seeing the world and learning from experience is good for them. The home schooling is only to satisfy the school back home so they won't be behind when they get home. Damn they're a lucky bunch!!