How to make a GUI's visibility set to false after a certain amount of time?

So here's what you'll need to do. First, if your script is a regular script, then change it to LocalScript, and insert that LocalScript into the target GUI.

Then, you must use a while true do which will make your script loop for eternity, you can even put a wait in there, so it waits every 10 seconds forever to change the GUI.

Next, identify your GUI properly with a good old script.Parent which will get the LocalScripts parent (What it's inside of).

Like this:

local guis = script.Parent

Then for the last touch. We must fix your script.

while true do
wait(10)
guis.Visible = false
wait(10)
guis.Visible = true
end

Hope this helped you!

I'm not sure but I would try this:

local guis = game.StarterGui.Menu.SideMenu

while wait(10) do
    guis.Visible = true
    wait(10)
    guis.Visible = false
end