This timekeeper comprises a first timer (4), means (12) for connecting it selectively to the train of the timekeeper (T), a second timer (5), a synchronous coupling between the first (4) and second (5) timers, and fly-back means (13, 13′, 9, 11) for said timers (4, 5). An auxiliary motive source (10′) is in a driving relationship with the second timer (5) and a one-way coupling (6a, 7a) is situated between the first (4) and second (5) timers to regulate the speed of movement of the latter at a predetermined ratio with the speed of movement of the first timer (4) while allowing one-way relative movement of the first timer (4) relative to the second (5) when the latter is in the stop position and one-way relative movement in the opposite sense of the second timer (5) when the first timer (4) is in the stop position.