resetAn overnight interval can be an hour shorter or longer when local clocks change. A start and finish that look 14 hours apart on the clock do not always represent 14 elapsed hours.
When clocks move forward
Suppose the local clock advances by one hour overnight. An interval from 8 pm to 10 am spans 14 hours by ordinary clock subtraction, but only 13 hours actually pass.
To count 14 elapsed hours from that start, the endpoint would be 11 am after the forward change. This is a calculation, not a reason to delay a meal.
When clocks move back
If the clock moves back by one hour instead, the same 8 pm to 10 am local times span 15 elapsed hours. One hour has occurred twice on the local clock.
The repeated hour can also make a manual entry ambiguous. A recorded 2:30 am may refer to two different instants, depending on the location’s transition rules. Avoid relying on the clock label alone.
Check the device and the record
Reset stores timestamps and calculates elapsed duration from them. Its display uses the phone’s local time context. If a duration looks unexpected after a transition, compare the start and end dates and check whether a clock change occurred between them.
Keep the phone’s time and time-zone settings accurate. Manually changing the device clock is not a useful way to correct a fasting record.
Know which tool you are using
The website’s schedule calculator works with a regular 24-hour day. It does not take a date or location, so it cannot know whether a daylight-saving transition applies.
For an interval around a transition, use date-aware times and check the actual elapsed duration. Our travel guide explains the same principle using UTC offsets.
If you need to eat earlier than an adjusted endpoint, record the actual end. The clock change is an explanation of a number, not a reason to override your wellbeing or clinical advice.