A graduation party is a milestone, but the restaurant deposit and final bill can hit your bank account all at once. Booking a private room six months out gives you the lead time you need to manage the bill without scrambling.
You want to focus on the graduate, not the invoice. Setting up a predictable payment plan now keeps the party from becoming a financial headache later.
The 0% window is a tool, not free money. If you have a remaining balance after 18 months, the card company will start charging interest on what you still owe.