When I change the hour for a weekly email report, the change is not taken into account for the next run but for the one after next.
I confirm this observation with the "Tasks Timetable" plugin.
Using Matomo 3.13.5
Bug still present in 3.14.1 version
I don't think we will fix this in a Matomo 3 at all. If this bug is still present in Matomo 4 it will get fixed there