Ivan Pavlov, the Russian physiologist, settled this issue over 80 years ago. He fed a dog punctually each morning for several weeks. Then, one morning, he withheld the dog's breakfast until after the usual time and watched closely for the dog's reaction. Within 20 seconds of the appointed time, the dog began to wag its tail and salivate - in anticipation of breakfast. Further tests confirmed that this was not an isolated incident.
Dogs have an extremely accurate ability to sense daily routines.
This ability to sense a daily pattern is not automatically a sign of intelligence, however. If you doubt this, remember that the same dog that goes crazy ten minutes before you get home from work is the same critter that wakes you up at five o'clock in the morning on Saturdays. The dog is capable of predicting a daily pattern, but incapable of understanding days of the week. If we assume that intellect is the ability to solve problems, the particular physical attributes of dogs can skew the test data. In the 1940's, blood hounds were tested against beagles to see which had the better sense of smell.