if you want it to be night time type in ".time 00:00" after that start playing with the colors of the fog/clouds to put it at your preffered settings.
Offline, you can have the time whatever you want (through all 24 hours). Online, once it reaches "dusk" it rolls right to "dawn". If you want real "night" online, set the time to 05:30 and the multiplier to 0 to freeze time.
I haven't set my light to black, and don't feel like trying...but if you go into the chconfig folder in your AH2 install, delete all your custom arena table files in the terrain folder you've been working in. That
should set everything back to default...I think.