The commissioner or his duly authorized representative may grant, modify or deny a petition for modification of abatement date filed pursuant to sections 804.2 and 804.3 of this Part. No determination of approval shall be made prior to the expiration of 15 working days from the date the petition was posted and served pursuant to section 804.4 of this Part. The commissioner will mail a copy of the determination to the parties which will also notify the parties of their rights under sections 804.7 and 804.8 of this Part.