After a schedule has been created and saved, it calculates its next run time, which is the value displayed in column Next Run Time when you are viewing the Schedule tab of a report. Each time a scheduled report runs, its next run time is recalculated.

If you later edit the schedule and change its frequency and/or its start time, the schedule must recalculate its next run time. It does so based on these rules:

If the schedule's frequency is changed to another value, the schedule refers to its Start date and time, and calculates the next run time which matches the new frequency, and that Start date and time. If that calculated next run time is in the past, the run time is advanced in increments until it is equal to or newer than the present date/time.

If the schedule's frequency is Hours and Minutes, and only the values of the Hours field and Minutes field are changed, the existing value of next run time will remain unchanged. However, when the report runs at that next run time, it will recalculate its run time, and during that recalculation the new values of Hours and Minutes will be used.