A new range changes how you cook every night. You get burners that actually light and an oven that stays at the right temperature. Swapping the old unit usually takes a pro less than an hour once it arrives. Late spring is the best time to do this because Memorial Day sales often have the deepest discounts of the year on appliances.
Don't just look at the sticker price on the floor. Get at least three quotes that include delivery, hauling away the old range, and a new gas line connector. Pros are often less busy in the weeks before the summer renovation rush, so you might have better luck scheduling the install.
This intro window is a firm deadline, not free money. If you still have a balance when the 18 months are up, the standard interest rate will apply to whatever is left. Pay the full amount before that clock runs out to avoid extra costs.