Error - Unable to cast value to object? Tweening descendants transparency.

Ok. So i'm trying to tween a bunch of descendants so that they appear at 6pm, and disappear at 7am. Its giving me an error on the line where I play() the tween, and for the life of me, I don't know why.

Please can you help?

Script is like this. I'm trying really hard to format it properly in this webpage and its not working. I'm sorry the formatting is wrong. Please help me.

local TweenService = game:GetService("TweenService")
local part = script.Parent.nightstuff:GetDescendants()

for _, part in pairs(script.Parent.nightstuff:GetDescendants()) do
	if part:IsA("BasePart") then 
		
		tweenInfo = TweenInfo.new(
			2, -- Time
			Enum.EasingStyle.Linear, -- EasingStyle
			Enum.EasingDirection.Out, -- EasingDirection
			0, -- RepeatCount (when less than zero the tween will loop indefinitely)
			false, -- Reverses (tween will reverse once reaching it's goal)
			3 -- DelayTime
		)
	
		TweenService:Create(part,tweenInfo, {Transparency = 1}):play()
	end
end

while wait(4) do
	for _,Player in pairs(game.Players:GetPlayers()) do
		if Player.Character ~= nil then
				if game.Lighting.ClockTime > 18 or game.Lighting.ClockTime < 7 then
				TweenService:Create(part,tweenInfo,{Transparency = 0}):play()
				print "transparency is now 0"
				end
			
		elseif game.Lighting.ClockTime < 18 and game.Lighting.ClockTime > 7 then
			TweenService:Create(part,tweenInfo,{Transparency = 1}):play()
			print "transparency is now 1"
			end
		end
	end