How to make a key cause delay from low bar?

So I'm trying to make a Magic script where when you press E it would make a Fireball/Create a forcefield but I want it to be used when limited so when a player presses the key once/twice, the bar would go down until it reaches lower than the required power for the magic, so it can delay that key or some sort while it refills until it's available. But it doesn't work very well for some reason.

local UIS = game:GetService('UserInputService')

local Bar = script.Parent:WaitForChild('Background'):WaitForChild('Bar')

local player = game.Players.LocalPlayer

local power = 10

local debounce  = false

repeat wait() until game.Players.LocalPlayer.Character

local character = player.Character

-----------------------------------------------------------------

UIS.InputBegan:connect(function(key, gameProcessed)
	if key.KeyCode == Enum.KeyCode.E and gameProcessed == false then
		debounce = true
		while power > 0 and debounce do
			power = power - 0.5
			Bar:TweenSize(UDim2.new(1, 0, power / 10, 0), 'Out', 'Quint', .1, true)
			wait()
			if power <= 0 then
				delay(5,key)
			end
		end
	end
end)

UIS.InputEnded:connect(function(key, gameProcessed)
	if key.KeyCode == Enum.KeyCode.E and gameProcessed == false then
		debounce = false
		while power < 10 and not debounce do
			power = power + .025
			Bar:TweenSize(UDim2.new(1, 0, power / 10, 0), 'Out', 'Quint', .1, true)
			wait()
			if power <= 0 then
				delay(5,key)
			end
		end
	end
end)

You should try using tick() this is a roblox function that returns how many seconds its been since 1970.

For example

local lastTick
if tick()-lastTick >= 5 or lastTick == nil then
    print("tada")
    lastTick = tick()
end