How to detect the player is clicking & holding ?

So i have a gui button and i want to create a easter egg function by clicking and holding it for 2 second This is a script i currently have in my mind

script.Parent.MouseButton1Down:Connect(function()
if script.Parent.MouseButton1Up then
else
wait(3)
--Secret function
end
end)

Idk if that works. Is there a better way of doing this ? Thanks for reading, hope you could help :D