Getting rid of that dated framed shower door opens up the whole bathroom and makes the space feel twice as big. The actual installation only takes a few hours, but you want to time it right by hiring local glass shops during their slower winter months when they are more likely to negotiate on labor. Call at least three different local shops for quotes so you know what the actual market rate is near you.
A standard custom frameless glass setup usually runs about $1100 installed. Doing this in the winter gets you past the spring remodel rush, and spreading out the cost helps you keep cash in your account for other things.
That 0% window is a hard deadline, not free money, so if any of the 1100 dollar balance is still sitting on the card when those 18 months run out, standard interest charges will kick in on whatever is left.