Can I leave and come back during a tour?

Probably not. Most tours, especially guided or timed-entry ones, don’t allow re-entry because they run on a schedule and need to control headcounts and security. Exceptions are rare—usually all-day self-guided venues like national parks, and even then you might need a wristband. Ask at the ticket desk before buying, and plan to bring snacks and use the restroom beforehand.