Displaying GUI for each player via RemoteEvent/RemoteFuntion?

The easiest way to do this is to already have the gui in each player's PlayerGui, and take advantage of FireAllClients.

FireAllClients is the same as using FireClient, except it fires all of them. Use this on a RemoteEvent in ReplicatedStorage from the server, and have a LocalScript on the client that recieves it using OnClientEvent.

Server:

--Game script?
local re = game.ReplicatedStorage.GuiStuff; --This is your RemoteEvent

while wait(60) do
	--codecodecodecode
	re:FireAllClients(true); --Send a bool argument for visibility
end

Client:

local re = game.ReplicatedStorage.GuiStuff --This is your RemoteEvent
local ui = script.Parent; --This is the gui

re.OnClientEvent:Connect(function(on) --'on' parameter for bool argument
	ui.Visible = on;
end)