What happens to scheduled jobs at the clock change?
In Schedule by Zaweba, a missing time runs once the clocks go forward, a doubled time runs once, and repeating jobs keep a true interval through the change.
With Schedule by Zaweba, very little happens that you need to worry about. When the clocks go forward, a job set for a time that does not exist that night runs as soon as the clocks have changed. When the clocks go back, a job set for a time that happens twice runs only once. Repeating jobs stay a true interval apart, so every 15 minutes means 15 real minutes all through the change.
Timetables follow the PC's local time, so the rest of the year a job set for 7:00 simply runs at 7:00 on the clock.
Why the clock change is a problem at all
A timetable is usually written in clock time, and on two nights a year the clock misbehaves. In spring an hour is skipped. In autumn an hour is repeated. Any scheduler has to decide what a time inside those hours means, and the wrong decision shows up as a job that never ran or ran twice.
Neither is harmless. A nightly backup that silently skips a night leaves a gap you will not find until you need it. A report that runs twice might email people twice or overwrite its own results. Because it only happens twice a year, these faults can go unnoticed for a long time.
Spring and autumn, night by night
Say a job is set for a time in the hour that gets skipped. On the night the clocks go forward, that time never appears. Schedule runs the job when the clocks have gone forward, so it still happens that night, just a little later by the clock than usual. The next night it is back at its normal time.
Now say a job is set for a time inside the hour that repeats. On the night the clocks go back, that time comes round twice. Schedule runs the job once. The second time the clock shows that time, nothing happens.
Jobs that repeat
For jobs that run every few minutes or every hour, Schedule follows real time rather than the clock face. Across the autumn change, a job every 15 minutes carries on at a steady 15 minutes and does not bunch up. Across the spring change it does not leave a gap either.
That is what you want from anything that polls, checks or syncs. The point of an interval is the interval.
How to check
Two parts of the app help. The timetable preview describes any timetable in words and lists the next 10 run times, so for a job that falls near a change you can see what is coming before you save. The run history records every run with what started it, its start and end times and its result, so the morning after a change you can see exactly what happened.
Other things that can look like a clock-change problem
Schedule runs as you, from the notification area, so jobs run while you are signed in to Windows. A job due in the night with the PC switched off did not run because of that, not because of the clocks. Catch-up can run a missed job once when Schedule is running again, and a job can wake the PC from sleep if Windows' Allow wake timers setting is on.
If you would rather never think about it, choose a time well away from the small hours, since the UK changes happen in the early hours of the morning. With Schedule, though, a time in the awkward hour is handled sensibly anyway.
In short
Missing times run once the clocks move, doubled times run once, intervals stay true. Schedule by Zaweba handles both nights a year on its own, and the history shows that it did.
