The Complete article:
http://animals.howstuffworks.com/pets/dogs-perceive-time.htm

I used to have a little spaniel and she would sit on the stair landing every day 15 to 20 minutes before everyone came home from work. We all ( 4 of us) worked different shifts every day so we never got home at the same time day to day. But she'd be there for each person to greet them when they got home.

Pavlov's dog.

I don`t know how she did it. For example my daughter would be due home at a certain time. But for some reason she didn`t get home when she was supposed to. No phone call or anything. The little spaniel would not sit on the landing until 15 to 20 min before she actually arrived. She was like that with everyone.

Very interesting article. I have always wondered about this with my dogs. It is just nice no matter how long I am gone whether it is for a short time or long they always come with wagging tails to greet me! Dogs really are a man's best friend, so so loyal.