That is exactly what my buddies do in the Alberta oilsands for exactly the overlap reason.

12 hour shifts are 13+ hours of actually being there because of lunch / breaks. For example Genentech in SF / Vacaville are "12 hours paid shifts" with 1 hour mandatory lunch. So no it is not required for an overlap because there i already a required by law break (lunch) that forces overlap (assuming this applies to more states than just CA).

This is the way it was handled when I worked in a place that had 3 8 hour shifts. You actually were there 8.5 hours with a 30 minute lunch, so this additional .25 hours just seemed odd that it was necessary.