40 CFR § 60.1785
What schedule must I follow for the stack testing?
June 9, 2020
(a) Conduct initial stack tests for the pollutants listed in §60.1775 by 180 days after your final compliance date.
(b) Conduct annual stack tests for the same pollutants after the initial stack test. Conduct each annual stack test no later than 13 months after the previous stack test.