I am trying to create a To-Be-Scheduled SLA for requests that need to be performed at a specific date, which we have a whole lot of. 

Jai provided me a script last week which works for changing the due-by date to any other date field, now I'm trying to trigger it at the right times. I thought I could just create a shared custom field named 'ScheduleDate' and trigger the script whenever that is populated on a template, but it doesn't appear that we can use date/time fields as the trigger (or multi-select, which is a bit more understandable). 

I'm guessing I'll have to create a separate custom field, and then use field and form rules to set that field when ScheduleDate is set, then trigger the script from that. That seems to be an extremely complex way of doing this.

Does anyone have a better solution for this?

Also, is there a particular reason we can't set due-by date in field and form rules? That would definitely be the easiest solution for what I'm trying to do.