A clean body panel makes a buyer take you seriously. Owning a car means swallowing the little maintenance costs that pile up over the years, and a minor dent can easily knock a few hundred bucks off your asking price.
Spring and early summer are usually when body shops are slammed with hail damage, so aim for late fall or winter when business slows down and techs have more room to cut you a deal. Negotiate the price of the repair first before you talk about how you plan to pay for it.
That intro window is a strict deadline, not free money. If you still have a balance left when the 18 months are up, deferred interest or standard rates will kick in on what remains.