Final answer:
The landing must be accomplished at or before 1929 if passengers are carried, as this fits within the aviation definition of night time for pilot night recency experience.
Step-by-step explanation:
For the purpose of calculating night recency experience flight time in aviation, night is defined as the period beginning 1 hour (1 hr.) after sunset and ending 1 hour (1 hr.) before sunrise. Based on the given scenario where the official sunset is at 1830, the permissible time window for a landing if passengers are to be carried must fall within this night definition.
Considering the additional hour required after sunset before it is officially considered 'night', the landing must be completed by 1929. Any landing later than 1929 would fall outside of the regulatory requirements for pilot night recency experience when carrying passengers.