Ten years is a big deal, and the weekend you spend celebrating it should feel like a moment for you both, not a weight on your bank account. Booking three months out gives you the best pick of flights and stays before prices climb for the season.
You can manage the $1200 cost by breaking it into manageable pieces before and after the trip. Planning early means you are not rushing or settling for whatever is left over.
Keep in mind that 0% intro APR is a deadline, not a gift. If you still have a balance after the 15 months are up, the card will start charging interest on whatever is left over.