A time schedule runs an action at a particular time, on selected days, or at regular intervals.
A daily schedule runs an action at the same time on selected days of the week.
A weekly schedule runs an action on a particular day of the week. You choose which weeks of the month the actions runs.
A monthly schedule runs an action once per month. You choose a time and day of the month, then select which months of the year the action will run.
An interval schedule starts at an arbitrary point in time and runs at regular time intervals thereafter.
If you desire actions to run at a particular clock time, use a daily, weekly, or monthly schedule. If you want actions to run at precise time intervals, use the interval schedule.
Daily, weekly, and monthly schedules work in local time. An action scheduled to run at 3:00 will run at 3:00 in the morning local time. If you change the time zone of your system, the action will adjust its start time accordingly. If your local time zone changes to/from daylight savings time, the schedule will adjust so that it continues to run at 3:00 in the morning.
Interval schedules works in absolute time. The start time you choose is stored internally in Coordinated Universal Time (UTC). Action run times are then calculated by adding exact time periods to that time. An interval of 1 day does not mean "one calendar day," it means "exactly 24 hours" (more precisely, 86,400 seconds).
An action with an interval schedule that runs at 3:00 in the morning in Tijuana, Mexico will run at 10:00 if the system is relocated to Dublin, Ireland (because 3:00 PST and 10:00 IST are the same time). Similarly, an action that ran at 6:00 the day before the transition to daylight savings time will run at 7:00 the next day.
Also see power management.