I've always thought the cats were by the door waiting for me because they could hear my car drive up. But since I have been home during the day, I've noticed Big (who is essentially my son's cat) starts pacing between the window that faces the parking lot and the window that opens to the patio about 15 minutes before my son's due home from school. Since I have no daytime rituals that are cueing him, it must be that he has a sense of time.