My cats also wait for us to get home and then use the box. And if one hears one of the other ones using it, they will stand by the box and when whoever is using it is done, they run out of the room and start chasing each other down the hallway and into the kitchen, sending litter flying all over my kitchen floor. Needless to say I have to sweep the floor daily.
My cats also love to use the box immediately after I clean them. They wait for me at the door as if they are telling me to hurry up and finish so they can begin!