A disabled systemd service with a "startAt" attribute, like this:
systemd.services.foo-service = {
enable = false;
startAt = "*-*-* 05:15:00";
...
};
will cause the following errors in the system journal:
systemd[1]: foo-service.timer: Refusing to start, unit to trigger not loaded.
systemd[1]: Failed to start foo-service.timer.
Fix it by not generating the corresponding timer unit when the service
is disabled.
(cherry picked from commit 2eb8aab42c)