No, you cannot extend your balance due date on your holiday booking. When you book your holiday, you'll need to pay a deposit and any top-up deposit must be paid on the date stated at the time of booking. The remaining balance of your holiday must be paid in full 10 weeks prior to the start of your holiday.
If you book less than 10 weeks before the start of your holiday, you must pay the full amount of the holiday at the time of booking.