I took the liberty to report this as a bug
Thanks Jonas. I figured this was by design, which is why I filed it as a request instead of a bug.
I understand. Talked it over with the team, and noone had a good argument for why it is that way.
This have now been fixed so that next execution date is always calculated based on the previous execution date (rather than when it was manually started). Should show up in a release the coming weeks.
Excellent, thanks Per!
For the record, the fix was introduced in Episerver.CMS.Core 10.3.0.
When starting a Scheduled Task manually, the next run date is automatically set to (now + specified interval).
Let's say there's a heavy job that syncs a whole bunch of data, which is set to run during the night. The job has gone FUBAR for some reason, so the admin runs the job manually during daytime to get the data up on the site. The next run date is now daytime the next day, which the admin may not notice.
Manually starting a Scheduled Task should not update the next run date.