Have you looked att the scheduled worksflows?

I agree, scheduled workflows would work need to see if it can interact with due date, if not then ask fresh to add it. 

diffInDays('{{current_date_and_time_iso}}','{{ticket.due_by_time_iso}}') <= 30

That is if it’s less then 30 days. you could change it to static 10 days.  == 10 
 

It’s this as well I think. The wording is a bit off 

So what i normally do with auto leaver, is say If “Leaving Date” is Less than today, then run at the scheduled time. 

I find due date on a ticket to be a little fussy with triggers and setting automatically, but you can use any date /time field on a ticket, as the trigger for a Scheduled workflow. 

ya, it can shift if the ticket set on hold, Better to use the date field on the service item. 

Yes, I would agree with you. Either using the specific Leaving date on the off boarding ticket, or the custom field on the service item. And then using tags or status to control things flowing. 

Trying to do this, too. I just get an error. I set it to 0 because I want the offboard to fire once the date and time is exact. What am I doing wrong? Says “Invalid Syntax - invalid return type for expression” - changed to Output = Boolean will work, but how does 12 days help, don’t we want it to be 0 so that it will do it on the exact date/time?