Del. Code tit. 18, § 3520

A group health insurance policy shall contain a provision that written notice of claim must be given to the insurer within 20 days after the occurrence or commencement of any loss covered by the policy. Failure to give notice within such time shall not invalidate nor reduce any claim if it shall be shown not to have been reasonably possible to give such notice and that notice was given as soon as was reasonably possible.