So, a little explanation about how vanilla works: normally, when you have a biter base in a pollution cloud, it will periodically start spawning an "attack wave" group. When the game judges the group big enough, they begin their attack. This process is completely unaffected by nightfall which also means daytime attacks are unaffected - unless you have "night attacks only" checked and the size of normal attack waves are completely unaffected.
If you do check "night attacks only," then the mod intervenes and puts a hold on those vanilla waves until nighttime (but an attack in progress won't be stopped).
Nightfall, in turn, searches for idle biters within a pollution cloud to form up into a group and launch attacks with. This happens with or without the option checked.