Penny has come over to escape from her girlfriend. Harold hears that girlfriend is "available" and leaves to go be with her. Penny plays Halo with the guys and winds up staying all night. In the morning while Penny is sleeping in Sheldon's spot, Sheldon tells Leonard that "every Saturday morning..." However, later in the show the guys go to ask Penny to play Halo because Wednesday night is Halo night.
Sheldon is wearing his Monday pajamas.
Also, Raj is talking to Leonard when Penny comes in. He continues to talk to Leonard even though Penny is in the room.