All operations in NCM work on Schedules.

You can define any number of schedules, and each schedule can have different periodicity.
(cron expression, or pre-made hourly, daily, monthly, etc.)

The Default Schedule

There must always be at least one Default Schedule in NCM.
(and one is automatically created for you when NCM runs for the 1st time)

You can't delete the Default Schedule.
If you wish to delete it, you must first choose a different schedule to be the Default Schedule.

Any operations that don't have an explicit schedule will use the default schedule.

You can change which schedule is the default schedule in the Schedules view.
Any operations which use the default schedule will properly be rescheduled to the new default schedule.

Explicit schedules

If you wish some devices to be polled differently (or some operations to run differently) from the Default Schedule, you can assign an explicit schedule to a device/operation.

Simply create a schedule in the Schedules view, and assign it to the device.
(either during the device creation, or Edit the device)

The same applies to NSM Sync, Mass Config Push, and Network Scan as well - you can use an explicit schedule in each of the respective features.

If you delete a schedule that is used like this, all operations that were using the schedule will be re-scheduled to the Default Schedule.