A tour guide's inability/unwillingness to adhere to the discipline of timing the tour is a sign of egoisme.
My bet is a key problem is our tour leader was not a professional tour guide. Instead, we took a field trip to a museum where you provide your own tour guide so we had a working scientist in the knowledge area leading us along with two retired scientists who had spent their whole careers in the very specialized area contributing stories along the way. As I told my husband, he would have loved this combination of The History Channel, Nova, Popular Science, and Old Guys Telling Stories. We had an incredible and unique experience that was definitely worth the day spent.
My frustration really is the 6 hours* when I was planning for 3 and yet we skimped on the one area that has direct relevance for my work and that's true for about half the other people on the tour. We have a running joke among my cohort of colleagues (all hired about the same time with different backgrounds and yet no one is an expert in this field) that we always start at the same date in history, go until someone runs out of breath, and yet we seldom even get up to things that happened in our lifetimes and we're over 40. Some bringing-up-to-speed discussions don't even get us up to the transistor being in wide use, which is problematic since we're doing high-tech machinery along with high performance computing and a lot has changed since before the time of the transistor.
* and no lunch! On top of my no breakfast because we left here at 0-dawn-30 to make the lengthy drive and then a late supper because of the lengthy drive back.