Once you've created your Ad and made the payment, your Ad is provisionally booked.
Your Ad would be released upon realization of your payment or receipt of your cheque number (if you've made your payment by a cheque) and your Ad ID.
Different Newspapers have different deadlines, depending on different focus days for certain categories. As long as the calendar allows you to select a particular date, you can book your ad for release on that date. But it is suggested that you complete your booking and clear the payments at least 2-3 days prior to the release dates.