Conversation so far:
when does it get dark in new york in december
Sunset in New York begins around 4:30PM in December.
how often does sunset occur
Sunset, also known as sundown, is the daily disappearance of the Sun below the horizon due to Earth's rotation.
how is the time of sunset defined
The time of sunset is defined in astronomy as the moment when the upper limb of the Sun disappears below the horizon.

Question: does the time vary
Self-contained rewrite: does the time of sunset vary