Where a person convicted desires to appeal under this Part of this Act to the High Court or to obtain the leave of the High Court to appeal, he shall within ten days of the date of his conviction in the case of appeal or application for leave to appeal against conviction, or within ten days of the date of his sentence in the case of appeal or application for leave to appeal against sentence, give notice of appeal or of application for leave to appeal. The time within which notice of appeal or of application for leave to appeal may be given may be extended at any time by the High Court.