This mod corrects the day of the year in the game's definition files, which in theory means that you'll get different temperatures at different times and the sun will rise and set sooner or later than the game's default.
If you don't want to redownload weekly, monthly, seasonally, you should probably download the TruckyMods Mod Manager so this mod will automatically update so you don't have to come here and manually reinstall this mod every day you play ATS