You may not deviate from the 13-month testing schedules specified in §113.2141(b) and §113.2143(b)(1) of this title (relating to What schedule must I follow for the stack testing? and May I conduct stack testing less often?) unless you apply to the executive director for an alternative schedule, and the executive director approves your request for alternate scheduling prior to the date on which you would otherwise have been required to conduct the next stack test.