One more time: FAR 135.267(c) is NOT applicable  

https://www.faa.gov/about/office_org/headquarters_offices/agc/practice_areas/regulations/interpretations/Data/interps/2017/Moody-SevenBar_Aviation_2017_Legal_Interpretation.pdf

Moody-Seven Bar Aviation (2017)

Question 2: Whether a certificate holder is able to operate under§ 135. 267 (c) if its flight crews commence their duty periods at a set time each day, but culminate their flight shifts at different times each day.

Subsection 135.267(c) applies exclusively to regularly assigned duty periods. When operating under§ 135.267(c), the commencement and conclusion of the 14-hour duty day should not vary on a daily basis. See Legal Interpretation to Daniel Berry, from Rebecca B. MacPherson, Assistant Chief Counsel for Regulations (May 22, 2009) and Legal Interpretation to John Barney, from Donald P. Byrne, Assistant Chief Counsel, Regulations and Enforcement Division (Dec 19, 1991) (Confirming that a regularly assigned duty period means a timefrarne where a pilot "comes to work and .. . goes home at the same time every day").

The FAA allows infrequent deviations from a regularly assigned work schedule conducted under§ 135.267(c).  However, "if the pilot's schedule has intermittent periods where the duty time fluctuates from day to day or week to week, the operator is not maintaining a regular work pattern." In such case, the operation should be conducted under§ 135.267(b). Therefore we must stress that if the flight crew's duty time fluctuates on a regular basis, it would not be able to operate under 135.267(c). See Legal Interpretation to Doug Holee, from Donald Byrne, Acting Assistant Chief Counsel, Regulations and Enforcement Division (July 22, 1989).