After issuing the initial GFE and waiting 10 business days, borrower makes contact on the 12th business day and provides intent. We issued a revised GFE - do we have to provide the borrower another 10 business days?

You don't have to 'wait' 10 days at all.
The GFE must be valid for a minimum of ten days.
You can chose to honor it and accept the borrowers intent on day 12 if you like.
You gave a new GFE so just ask if they still want to proceed.