I stand corrected, it came to me when I went to bed that the time differential is 40 minutes, not 10

Revising my calculation, if sunset at Chattanooga for September 19, is stated as 7:43 EDT, actually 6:43 EST, it would be 6:03 PM local, solar time.

http://sunrisehour.com/sunrise-sunset/united_states/chattanooga_tn

Or, as you state, the officer said it was 7 PM. That being local, would mean present day time 7:40 EST, or 8:40 EDT. An hour after sunset.

This could be well into darkness. Even more so if there are hills/mountains to the West, or if you’re in a valley, remembering that tabular sunset is the time the sun sets below the visible horizon as one would see at sea. Apparent sunset, with it’s accompanying darkness, would thus, be somewhat earlier than predicted for the location.