How do I make a textbutton that appears after x time?

First thing I notice is that you're calling StarterGui. Changing things in StarterGui during the game won't affect the player's Gui.

So how do we change the player's Gui? The answer is simple. Inside a local script, we need to first find the player.

--inside a local script
local Player = game.Players.LocalPlayer --Getting the local player from the service Players.

Then we simply locate the Gui from Player and change the property.

--inside a local script
local Player = game.Players.LocalPlayer --Getting the local player from the service Players.

Player.PlayerGui.ScreenGUI.Frame.TextButton.Visible = false

So here's the finished product.

--inside a local script
local Player = game.Players.LocalPlayer --Getting the local player from the service Players.

wait(3)

Player.PlayerGui.ScreenGUI.Frame.TextButton.Visible = false

EDIT An easier solution would be making a local script just inside the TextButton and writing this:

--inside a local script
local button = script.Parent
wait(3)
button.Visible = false

Remember that since the Gui is in StarterGui, it'll already be replicated to the PlayerGui for you.

I think your code should work to be honest..

local gui = *Your Gui Path*
wait(3)
gui.Visible = true

The above code should work but maybe another setting is disabled. For instance, the Enabled property.

My solution would be to instead of making it visible, cloning it from ReplicatedStorage or ReplicatedFirst(whatever fits your needs more), and then destroying the gui when you are done with it. It is much easier because no settings have to be changed, literally just:

local gui = *Your Gui Path*
local player = game:GetService("Players").LocalPlayer

wait(3)

local clone = gui:Clone()
clone.Parent = player.PlayerGui

wait(3)

clone:Destroy()

Of course, you don't need to wait to destroy, you could make a button when pressed do that. Sorry if the code is wrong, I just wrote it really fast. You make the decision which is better for you, and I hoped I helped!

Edit: OH, you also forgot to add brackets to the tick