I was looking for a way to tweak flight simulator to make the VC lights to display earlier in the day, and I ran into a forum post from 2016 on flightsim.com that explained the solution.
"I was able to get my FTX and UTX lights to turn on about 40 minutes earlier using the following in the FSX.cfg:
[GRAPHICS] DAY_THRESHOLD=50000 //min 0, max 65535 NIGHT_THRESHOLD=4096
The higher the DAY_THRESHOLD value the earlier the lights come on, a value of 40000 vs 50000 appears to amount to about 10-12 minutes difference in the sim. Using yesterday's sim date near Washington DC the FTX lights were turning on at 20:09 local time without the tweak, with a DAY_THRESHOLD value of 50000 the lights would come on at roughly 19:35. At 19:35 the ground textures were just starting to light up and without the tweak you'd fly around for 35 minutes before the actual FTX/UTX lights would turn on, the tweak changes that so the lights come on while it's still relatively daylight which to me looks more realistic.
To implement this tweak simply open the fsx.cfg in notepad and add the two lines anywhere under the [GRAPHICS] header, save. Start a flight, choose "day" then "dusk" and then roll back the clock about an hour, fly until you see the lights come on, note the time and ambient lighting. Play with the DAY_THRESHOLD value to suit your tastes.
There may be unwanted side effects, for example it seems to also effect the time that the aircraft panels light up. That in itself didn't seem like a problem to me but quite possibly there may be other side effects I haven't seen yet.
Works in P3D as well (you can use "time preview" in P3D for adjusting the DAY_THRESHOLD value, works great)." - Jim Robinson, VIP Member, Flightsim.com -
I personally tried this tweak in P3Dv4.1, and it works!