Think about the number of pets doing this at, say, 20:07, and owners not realizing the time accuracy because it's not a round number of minutes after the hour.
There are circadian rhythm genes in c. elegans that take effect even when under artificial light. Also the skill for this is trainable.
At school we used to have a bell mark class ends and without a clock or a watch I could predictably tell when the bell would fire. One time I demonstrated this to a friend (both of us kicked out of class) by counting down from 10 on the second to when the bell rang while looking at a blank wall.
