In principle, the court will not consider appeals lodged too late and will declare such appeals to be inadmissible. Exceptional circumstances may lead to an excusable failure to meet the term. This means that the party bringing the appeal has good reasons to be late.
Should you, for whichever reason, be unable to meet the appeal requirements, you may bring a so-called pro forma appeal. This allows you to bring your appeal within the set period. Pro forma appeals are usually brought to gain more time to properly and carefully substantiate the appeal. The court will allow you to submit this substantiation within a certain term, usually of two to four weeks.
The above provisions are covered by Section 6:11 of the General Administrative Law Act ((excusable) failure to meet the term) and Section 6:6 of the General Administrative Law Act (cure period).