The FAA released a clarification concerning the definition of a Nighttime operation.
A nighttime operation is simply an FDP that is scheduled to infringe on the WOCL.
Thus, if a FCM is scheduled for 4 FDP’s where FDP’s 1, 2 and 4 are scheduled to infringe upon the WOCL with no scheduled mid-duty break of 2 hours or more, and FDP 3 is scheduled to end before the start of the WOCL the FCM is legal.
If FDP is delayed and ends after the start of the WOCL the FCM is still permitted to operate FDP #4.
The FAA cautions that FDP #3 must have been realistically scheduled not to infringe upon the WOCL.
Understanding FAR 117 