How far in advance should I purchase Dream Wedding Insurance for my wedding to be covered?

How far in advance should I purchase Dream Wedding Insurance for my wedding to be covered?
Dream Wedding Insurance

You can purchase Dream Wedding Insurance up to 18 months prior to the wedding day. If purchased less than 30 days before the Wedding Event, Section 1: Wedding Event Cancellation, Postponement or Rescheduling shall be excluded. The policy coverage will cease at the completion of the wedding event.