If there isn't something that requires his attention as Superman, then he's been known to go as Clark Kent and have breakfast with his co-workers. Usually it was as Dooley's coffee shop. But he's never shirked his responsibilities unless he had a stand-in for him, when he couldn't. I cannot speak for the Pre-Crisis tales like the above posted, but I can for the Post Crisis era.
It doesn't really matter if Superman sleeps in. He can just fly backwards around the Earth and rewind time. So hey, he may sleep in all the time and we just don't know it :)
The coffee shop is made up of materials salvaged from an (untold) encounter with the Zoners when General Lane was duped into sending Kal into the Zone. As a result of the events in the Zone, the properties of the various materials were altered and took the (maleable) form of several constructs (a building, a car, and a 'pda').
I think I remember that in either Miracle Monday or Last Son of Krypton Maggin wrote that Superman did need to sleep, and did sleep every night,-- usually for like two or three hours, and then he was well rested.
I envision it as a real "Axe Cop" situation.
You know, kinda like that.
That doesn't preclude that if something needs his attention, he won't forego sleep to do what needs to be done.
Bring back X-23's series petition
Bring back X-23's series facebook page
"Make yourself comfortable, I haven’t time to attend to it." - With these words, a legend was born.