Hello,
So some notes about this - two things are required for it to work.
- Biters have to be in pollution. Those not under a pollution cloud won't attack. (Sounds like you do have at least a few in pollution).
- It has to be able to find "spare" biters - the mod does not spawn its own attack waves.
These 2 factors basically mean it scales with the map's difficulty settings and how much pollution from your factory is reaching the biters. If there's not many biter bases under a pollution cloud and/or the map settings for biters are low, there won't be much extra.
If you want a more comprehensive package that really scales up biter difficulties, I recommend Rampant (I play with Rampant fairly often myself). Nightfall is more of a very slight tweak to vanilla that just makes the existing biters more aggressive at night.
But if you do want a little increase in challenge without more mods, you can check "Only attack at night." This is harder because the biters still build up during the day - and then throw everything at you at night. Where without this they attack you in smaller groups throughout the day, and will send more at night if there are biters available (but with a large pollution cloud and a number of active biter bases, there near certainly will be).
On the flipside, though, if you have super defenses... well, Rampant's built more for stuff like that. Rampant's biters can probe your defenses and look for weak spots and so on.
