Night Time

What is the best way to make it appear to be night time on any map, without causing a significant fps drop?

How realistic do you want the nighttime to be?
I’ve seen a gamemode use Colormod and it did the trick. I’m not sure about how much it costs performance-wise.

It doesn’t have to be entirely realistic, it just can’t blind the players.

Well you could try adjusting the environment_lighting or whatever its called in a map. Of course the map has to have this, to work.