Can some help change material at Time A and Time B?

Can someone help me edit this script to change to Neon when it reaches a certain time, but changes back to SmoothPlastic when it reaches another certain time?

local Lighting = game:GetService("Lighting");

-- Our while loop
while true do

-- Checking if the time is 18 or more.
if Lighting.ClockTime >= 18 then

    -- Let's change the lamp's material to Neon!
    script.Parent.BrickColor = BrickColor.new("Pink")

    else

    -- Change it to SmoothPlastic if it isn't late :D
    script.Parent.Material = Enum.Material.SmoothPlastic;
end

wait(1) -- Waits a second before continuing
end

pink isnt a material, its a colour.

local Lighting = game:GetService("Lighting");
while true do
	if Lighting.ClockTime >= 18 then
   		script.Parent.Material = Enum.material.Neon
		script.Parent.BrickColor = BrickColor.new("Pink")
   		else
    		script.Parent.Material = Enum.Material.SmoothPlastic;
	end
wait(1)
end