Many travel insurance policies have certain benefits that are date sensitive.  These benefits may include financial default of a travel supplier, a pre-existing condition exclusion waiver, cancel for any reason,  cancel for work reasons and terrorism.  Some polices require that the insurance policy be purchased within a certain number of days (typically 14 - 21 days depending on the policy selected)  from the very first payment toward your trip in order to have cover or options for these benefits.