Several manufacturers list in their manuals the night-time hours when the date should not be changed, and those hours vary from one calibre to another.
The United States turns its clocks back one hour on Sunday, November 1, as do the municipalities along Mexico's northern border that still change their clocks twice a year; the rest of Mexico stopped doing so in 2022, and Spain made the change on October 25. Resetting a watch raises a practical question: at what time of day can the date on a mechanical watch be changed without risk of damage? Several brands answer it in the manuals for their calibres.
What happens before midnight
In a mechanical watch, the date is printed on a disc numbered 1 to 31 that sits beneath the dial. The disc moves on one number a day, driven by a wheel that turns with the hands and makes one full revolution every 24 hours. That wheel carries a part called a finger, which starts pushing the disc several hours before midnight; close to 12, the disc jumps to the next number, and the finger moves clear of it a little later. So the date change takes up several hours of the night.
On watches with a quick-set date, the crown in its first position advances the same disc without moving the hands. Used while the finger is also pushing the disc, it puts two forces on it at once, and one of its teeth or the finger itself can bend or break. It is a little like trying to turn the page of a book while another hand is holding it halfway: the paper can tear. Seiko warns in the manual for its 4R35 and 4R36 calibres that changing the date during those hours may stop it from advancing the next day, and may even damage the mechanism.
The hours for each calibre
The hours when it is best not to change the date vary from calibre to calibre, because each mechanism starts and finishes the change at different times, and each manufacturer gives them in its manual. The table below brings together several calibres. In the Seiko 5 Sports SKX, sold in Latin America and Spain, the 4R36 calibre shows the day of the week and the date, and its restricted period ends later than that of the 4R35, which shows the date only.
Eterna offers an alternative for its watches with the Swiss Sellita SW200 calibre: during those hours, the date can be advanced by turning the hour hand, without using the quick-set.
What each manual says
| Seiko 4R35 (date) | Do not change the date between 9 p.m. and 1 a.m. |
| Seiko 4R36 (day and date; Seiko 5 Sports SKX) | Do not change the date or day between 9 p.m. and 4 a.m. |
| Sellita SW200 (Eterna manual) | Do not use the quick-set between 10 p.m. and 2 a.m.; during those hours, the date can be advanced by turning the hour hand |
| Mido Calibre 80 GMT (ETA C07.661 base; Ocean Star GMT) | The date is changed with the hour hand, in one-hour jumps; do not change it between 10 p.m. and 2 a.m. |
| Rolex GMT-Master II | The date is changed with the hour hand, forwards or backwards, as it passes midnight; the manual gives no restricted period |
| Patek Philippe 240 Q (perpetual calendar) | Do not correct the calendar or moon phase between 4 p.m. and 1 a.m.; do not turn the hands backwards past midnight |
GMT watches and perpetual calendars
On several GMT watches, which show the time in a second time zone with an extra hand, the date has no quick-set of its own. It is changed by moving the hour hand in one-hour jumps, forwards or backwards, and the date changes each time that hand passes midnight. The Rolex GMT-Master II and the Mido Ocean Star GMT work this way. Mido's manual still asks for the date not to be changed during the period shown in the table.
A perpetual calendar shows the correct date without needing manual adjustment through 30- and 31-day months, February and leap years. It also has the longest restricted period in the table. For its calibre 240 Q, Patek Philippe recommends not turning the hands backwards past midnight, because the calendar displays would fall out of step, even though the mechanism would not be damaged.
The most common mistake
The periods in the table refer to the time shown by the watch's hands, which does not always match the actual time, and forgetting this is the most common mistake. On a 12-hour dial, 10 in the morning and 10 at night look the same. If an automatic watch has stopped with its hands at 10, its mechanism may be at 10 p.m., inside the restricted period, even if it is being set in the morning.
How to set the date, step by step
On an automatic watch with a quick-set date, this sequence avoids changing the date during the restricted period. It combines the procedure in Seiko's manual with the periods in the table:
- If the watch has stopped, wind it. If the crown screws down, unscrew it.
- With the crown in the time-setting position, move the hands to 6 o'clock. Whether it is morning or evening, that time falls outside the restricted periods of the simple-date watches in the table.
- With the crown in the quick-set position, set the date to the previous day.
- Back in the time-setting position, advance the hands until the date changes to the next day. That change shows the watch has just passed midnight and is now in the morning.
- Keep advancing the hands to the correct time, adding one more full turn if it is afternoon or evening, then push the crown in and screw it down if needed.
For the November 1 clock change, turning the hour hand back one hour during the day, well away from midnight, is enough, and the date stays where it is.
The hours when the date should not be changed are the ones the watch itself takes up with the date change, and the manual for each calibre lists them. ORELO explained how the local hour on a GMT is changed without stopping the watch in its article on the Baltic Aquascaphe GMT MK-II.
The hours and steps described here are general guidance, based on the manuals of several manufacturers. Each watch may have its own instructions, and whenever possible the safest reference is the manufacturer's manual, which is usually available on the brand's official website.
