Workflow trigger notification for warranty expiration

We run Sugar OnDemand 7.11.1.  I need to trigger an Account module email notification 45 days prior to a warranty expiration date field value.  This would need to be for all Account module records where the warranty expiration date is not empty and is not dependent on a modified or updated field value.  I'm curious if it could be accomplished using a custom field (maybe hidden field) to calculate the date 45 days prior to the field value in the warranty expiration date field, Workflow and/or a daily scheduled report that is then used as a trigger for email notification based on the calculated field.  Any direction would be appreciated.

Thanks