Instead of using a Permanent_Monster_Spawn, you could use a script:
OnInit --> spawn X monsters (use the monster script command)
spawn the monsters with an attached even label
when the monster dies, that label triggers --> (re)spawn 1 more monster
add the OnDay and OnNight source edit
OnDay --> killmonster (kill the monsters with your event label)
OnNight --> respawn the monsters (same trigger as OnInit)
Example:- script night_only_mob_spawns -1,{
OnInit:
OnNight:
killmonster "prontera", strnpcinfo(3)+"::OnZombieDead";
monster "prontera",155,180,"Zombie",1015,10,strnpcinfo(3)+"::OnZombieDead";
end;
OnZombieDead:
if (isnight())
monster "prontera",155,180,"Zombie",1015,1 ,strnpcinfo(3)+"::OnZombieDead";
end;
OnDay:
killmonster "prontera", strnpcinfo(3)+"::OnZombieDead";
end;
}