I need help with spawning a zombie during night?

I tried making a zombie spawner for night time only and making sure its max 6 zombies however, It doesn't seem to work can anybody help me?

local NPC = game.ReplicatedStorage.Zombie
local spawner = game.Workspace.ZombieSpawns.XSp
local xox = game.ReplicatedStorage.Zombie.UpperTorso
local posXsp = game.Workspace.ZombieSpawns.XSp.Position
local lol = game.Workspace

while true do
	if game.Lighting.ClockTime >= 17 and game.Lighting.ClockTime <= 6 then
		local Colne = NPC:Clone()
		Colne.xox.CFrame = CFrame.new(posXsp) + Vector3.new(1,0,0)
		Colne.lol = posXsp
	end
end