How do you make SurfaceGUI/GUI tween, longer for a specific time?

So I made a tween size script for my simple SurfaceGui animation. My question is how do I make the tween size function run for a specific time so I decide when the gui part will reach my prefered tween possition?

My code:

local Frame = script.Parent.Frame
local StartButton = script.Parent.Frame.Start
local GUIBar = script.Parent.Frame.ProgressBar

function OnClicked()
    StartButton.TextScaled = true
    StartButton.Text = "In progress..."

    GUIBar.Size = UDim2.new (0, 0,0, 50)
    GUIBar:TweenSize(UDim2.new (0, 600,0, 50))

end

StartButton.MouseButton1Click:connect(OnClicked)

What do I need to do here?