Does anyone know how this works for drivers that today drive for both Uber and Lyft at the same time? I see many cars with both stickers on the windshield, and

Does anyone know how this works for drivers that today drive for both Uber and Lyft at the same time? I see many cars with both stickers on the windshield, and it seems like a very powerful force preventing one or the other from gaining a monopoly status in the city. When a driver using both apps is waiting for a ride, whose time are they clocking under? Does that create legal incentives for drivers to drive for one company, and in doing so make it very hard to sustain minority competitor in the ride sharing space?