You are picturing the night before the wedding: good food, close friends, and zero stress in a quiet back room of your favorite spot. Getting that exact scene locked down takes a bit of planning, especially when you are trying to balance the deposit with the rest of the wedding bills.
Since this is a fixed date on the calendar, lead time is your best tool for keeping costs normal. We need to lock in the space early so you aren't stuck paying rush prices or scrambling for leftovers.
That intro window is a hard deadline, not free money. If you still have a balance left on the Citi Simplicity® Credit Card when the 0% for 18 months on purchases and balance transfers from date of account opening period ends, the remaining amount will start getting hit with regular interest.