As I said previously, this mod was made as 'an addition' to the Autumn Mod and only with that mod it makes complete sense as to give you the feeling that the autumn is really there ;)
The duration of the weather won't change because if it would be shortened then the whole beauty of sunrise/sunset would be lost. In real life it looks exactly like that. When it's dark, it's dark for some longer time and not 15 min, etc.
And to be honest, this mod is for those who really play Test Drive. Those who spend like +/- 30min a week will be disappointed as the game 'saves' last position of the weather. This means that when you lunched the game and it was night, been playing like 15-20 min and then you go back to TDU after a couple of days you'll get the night.
As I said - this mod makes TDU a brand-new experience ;) some of you will love it, some don't ;)
Cheers! :)