(3)The appeal shall be presented within a period of thirty days from the date of service of the notice of demand relating to the assessment or the date of service of the order, as the case may be, but the appellate authority may admit an appeal presented after the expiration of the said period if it is satisfied that the appellant had sufficient cause for not presenting it within the said period, provided however that no such appeal shall be admitted after a period of six months from the date of service of the notice of demand relating to the assessment or the date of service of the order, as the case may be.
