global static ffrr.ProcessScheduleService.RunDueSchedulesResult runDueSchedules()

This method will run any due process schedules. Due process schedules are schedules where the NextDue__c date/time is in the past.
If the process schedule successfully started its automation configuration, the NextDue__c date/time is recalculated to find the next due date.
The process schedules that are due are ordered by the earliest NextDue__c first.
Note it is possible to have multiple process schedules be due for the same automation configuration. In this scenario the method will attempt to run the automation configuration multiple times which might result in some processes clashing.
Due process schedules will only be run by this method. If this method is only called infrequently, this might mean there is a significant delay between the schedule becoming due, and its automation configuration actually being run. We recommend your implementation runs the method at a regular cadence.