Most oil boilers are oversized for the heating load since even a 3 section boiler (smallest oil boiler) is too big for an average insulated home. If there is hot water for showers, etc. the burner will run for longer.
Our 3 section Peerless WBV boiler has burner on times of between 5 and 10 minutes in the middle of the winter when we are not using the hot water. The house is about 2400 square feet on Long Island.