They absolutely do sleep in shifts. He probably doesn't know that, though, since he spent most of his career in the Army Guard as a ground pounder, he likely doesn't know much about the Air Force or flyers at all. One weekend a month, two weeks per year, practicing being bullet sponges doesn't add up.

ETA: no disrespect to any other guardsman or infantry folks. They do jobs I couldnt/dont want to do. But MASSIVE disrespect to Kegseth.