Well, they don't necessarily sleep at night, but they do sleep.
"When the workers penetrate the cells, and remain fifteen or twenty minutes motionless, I have reason to believe, it is to repose from their labours. My observations on the subject seem correct. You know, Sir, that a kind of irregular shaped cells, are frequently constructed on the panes of the hive. These, being glass on one side, are exceedingly convenient to the observe, since all that passes within is exposed. I have often seen bees enter these cells when nothing could attract them. The cells contained neither eggs nor honey, nor did they need further completion. Therefore the workers repaired thither only to enjoy some moments of repose. Indeed, they were fifteen or twenty minutes so perfectly motionless, that had not the dilation of the rings, shewed their respiration, we might have concluded them dead. The queen also sometimes penetrates the cells of the males, and continues very long motionless in them. Her position prevents the bees from paying their full homage to her, yet even then the workers do not fail to form a circle around her and brush the part of her belly that remains exposed."--Francis Huber, New Observations Upon Bees