Do dolphins sleep in the day or the night?

Yes. All creatures must sleep. The dolphin can sleep, move and breath at the same time.

They do this by allowing only half of their brain to shut down. They often can get about 8 hours of sleep. They can accomplish this three ways. They can slowly cruise at the surface of the water taking breaths, they can rest at the bottom of a shallow area rising to the surface to get a breath or they can simply rest on the surface. Dolphins do sleep, but in a very unique way. One half of the brain dozes off, whilest the other is still awake (looking out for predators) then vice versa (happens to the the other side) Hope it helps =)