[SalesForce] Scheduled action in process builder

Workaround is to return a list even if the list isn't being used, according to known issues, will be fixed in Summer 15 release.

The criteria will still apply, as long as the process evaluates both insert and update. See How Does Salesforce Process Scheduled Actions?:

What Happens When the Field Values Change?

• For processes that start when a record is created or edited, scheduled actions remain in the queue only as long as the criteria for those actions are still valid. If a record no longer matches the criteria, Salesforce removes the scheduled actions for the record from the queue.
• For processes that start when a record is created, Salesforce never reevaluates the record with that process. Scheduled actions remain in the queue, even if the record no longer meets the associated criteria when the scheduled actions are executed.

• If you change the referenced field value and the schedule hasn’t been processed, Salesforce recalculates the schedule associated with the field.

  For example, a process is configured to email an opportunity owner 7 days before the opportunity close date. The close date is set to 2/20/2014. Salesforce processes the schedule on 2/13/2014 and sends the email. If the close date is later updated to 2/10/2014 and the schedule hasn’t been processed yet, Salesforce recalculates the schedule and sends the email on 2/3/2014. If Salesforce recalculates the schedule to a date in the past, it executes the associated actions shortly after you save the record.

• If the record or object that the schedule is associated with is deleted, Salesforce never processes the schedule.