Schedule page "Next time" shows one day too early even after PR and more

See [Schedule page "Next time" shows one day too early even after PR](https://github.com/duplicati/ngclient/issues/469#issuecomment-5035886116) with a rather confusing history.

Also [Release: 2.3.0.107 (Canary) 2026-07-13](https://forum.duplicati.com/t/release-2-3-0-107-canary-2026-07-13/22545/16?u=ts678) with other confusing history.

If you prefer to reopen the issue that prior work was done on, that's fine. Lacking reopen, I filed again.

This bit me again today on 2.3.0.108_canary_2026-07-20 after option edit. Submit and it runs instantly.

Start by reading the linked issue 469 comment and the referenced Duplicati forum thread, then reproduce the problem on 2.3.0.108_canary_2026-07-20 by editing an option and submitting the schedule. Done means the Schedule page's “Next time” value is no longer one day early and does not report a run as immediate when it should not.

Written by the indexing model from the issue text.