I would like to set a deadline for a workflow, but I would like to base it upon a field date rather than the starting date of the entry in the workflow.  How can I accomplish this?

Example...

I have a permit that is issued, but sometimes it does not get entered into Laserfiche right away.  When the scanner operator scans the permit, the actual permit application date is entered as a field.  I would like to base the deadline on this rather than the starting date of the workflow.