It is said that dogs do not have a good sense of differences between medium lengths of time. For example if you leave puppy at home, and go to the store for an hour, from the dog's point of view it really can't tell whether you have been gone 1 hr or 2-3 hrs. So most likely 2 hrs before does seem like din din time to them.

Two years is a lot of behavior to overcome. You might try working on them to stay, and rewarding with a treat. But don't give them peanut butter-apple treats... it will spoil their dinner.