At any time after the adoption of a resolution granting a variance, any person having an interest in such decision may move the board for an order vacating or modifying any term of condition of said decision by filing with the board a petition in the form of a letter setting forth the reasons therefor and the grounds relied upon. If the petition is granted, the board shall fix a date for hearing, and the movant shall give notice of such hearing in the same form and manner as required in the case of original petitions. The board, on its own motion, may in a proper case similarly order all parties in interest to show cause at a time and place fixed in the notice why the terms or provisions of any variance ought not to be vacated or modified.