Simple timer for Roblox

local plr = game.Players.LocalPlayer
local gui = Instance.new("ScreenGui")
gui.Parent = plr.PlayerGui
gui.ResetOnSpawn = false
local timer = Instance.new("TextLabel")
timer.Parent = gui
timer.BackgroundTransparency = 1
timer.Size = UDim2.new(0.125, 0, 0.125, 0)
timer.Position = UDim2.new(0, 0, 0.5 ,0)
timer.TextXAlignment = Enum.TextXAlignment.Center
timer.TextScaled = true
timer.Text = "00:00:00"
timer.TextColor3 = Color3.new(255, 255, 255)
timer.Font = Enum.Font.Code
local x = 0
local y = 0
local z = 40
while wait(1) do
    if z >= 60 then
        y = y + 1
        z = 0
    end
    if y >= 60 then
        x = x + 1
        y = 0
    end
    local tz = "00"
    local ty = "00"
    local tx = "00"
    if z >= 10 then
        tz = z
    else
        tz = "0" .. z
    end
    if y >= 10 then
        ty = y
    else
        ty = "0" .. y
    end
    if x >= 10 then
        tx = x
    else
        tx = "0" .. x
    end
    timer.Text = tx .. ":" .. ty .. ":" .. tz
    z = z + 1
end