Del. Code tit. 18 § 3522
When applicable, a group health insurance policy shall contain a provision that in the case of claim for loss of time for disability, written proof of such loss must be furnished to the insurer within 90 days after the commencement of the period for which the insurer is liable, and that subsequent written proofs of the continuance of such disability must be furnished to the insurer at such intervals as the insurer may reasonably require, and that in the case of claim for any other loss, written proof of such loss must be furnished to the insurer within 90 days after the date of such loss. Failure to furnish such proof within such time shall not invalidate nor reduce any claim if it was not reasonably possible to furnish such proof within such time, provided such proof is furnished as soon as reasonably possible and in no event, except in the absence of legal capacity of the claimant, later than 1 year from the time proof is otherwise required.
18 Del. C. § 3522