Rescheduling of Email Campaign is possible for Simple Schedule, Batch Schedule, and RSS Schedule before one hour (60mins) ahead of the execution date. 

The user will be required to visit the Marketing > Email. Please visit the Email Campaign tab, it will have a list of Email Campaigns listed with Simple Schedule, RSS Schedule and Batch Schedule which can be rescheduled before one hour of execution date/time.

In the action button, there will be the option of Reschedule Campaign. The user can make the changes to the details of the Schedule and change the delivery model. Once the changes are done, the user is required to mark it as the rescheduled campaign to save the settings.