How to make a script compatible for multiple players?

Okay i'm making a game which has rounds. I scripted the round system but it only works with one player. How can I make this work when there are multiple players on the server. By work I mean make all the timers the same for every player whose in the game.

Here's my script:

game.Players.PlayerAdded:connect(function(player)
	function intermission()
		game.workspace.Music:Play()
		GUI = player.PlayerGui:WaitForChild'Intermission'.Frame
		NewsGUI = player.PlayerGui.NewsBar.Frame
		NewsGUI.Visible = true
		Second = GUI.Seconds
		GUI.Visible = true
			for i = 45,1, -1 do
				Second.Text = i
				wait(1)
				  if Second.Text == "1" then
			       map = game.Lighting:FindFirstChild("MAP1"):clone()
			       map.Parent = game.workspace
			       map:MakeJoints()
			       GUI.Seconds.Text = " "
			       GUI.Title.Text = "Loading Map"
			       wait(7)
			       player.Character.Torso.CFrame = CFrame.new(Vector3.new(967.119, 41.396, -391.16))
			        RoundBegin()
			      end
			end
	end
	
	function RoundBegin()
		GUI = player.PlayerGui:WaitForChild'Intermission'.Frame
		GUI2 = player.PlayerGui:WaitForChild'StartRound'.Frame
		GUI3 = player.PlayerGui:WaitForChild'RoundTime'.Frame
		NewsGUI = player.PlayerGui.NewsBar.Frame
		game.workspace.Music:Stop()
		game.workspace.RoundMusic:Play()
		Second2 = GUI2.BeginTime
		Second3 = GUI3.TextLabel
		GUI.Title.Text = "Intermission"
		GUI.Visible = false
		GUI2.Visible = true
		NewsGUI.Visible = false
		for i = 5,1, -1 do
			Second2.Text = i
			wait(1)
			  if Second2.Text == "1" then
				GUI3.Visible = true 
				GUI2.Visible = false
				game.Workspace.RoundMusic:Stop()
				  for i = 300,1, -1 do
					Second3.Text = i
					wait(1)
				end
				RoundEnd()
			end
		end
		
	end
	
	function RoundEnd()
		GUI3 = player.PlayerGui:WaitForChild'RoundTime'.Frame
		GUI4 = player.PlayerGui:WaitForChild'RoundEnd'.Frame
		
		GUI3.Visible = false
		GUI4.Visible = true			
		map:Destroy()
		player.Character.Torso.CFrame = CFrame.new(Vector3.new(4, 4.938, -53.5))
		wait(5)
		GUI4.Visible = false
		
		intermission()
	end
	
	intermission()
end)

Well you're editing their timer when they join, just use a for loop and get all the Players from it and use it to edit the GUI in their PlayerGui eg -

function intermission()
        game.workspace.Music:Play()
	for i,v in pairs(game.Players:GetPlayers()) do
        GUI = v.PlayerGui:WaitForChild'Intermission'.Frame
        NewsGUI = v.PlayerGui.NewsBar.Frame
        NewsGUI.Visible = true
        Second = GUI.Seconds
        GUI.Visible = true
            for i = 45,1, -1 do
                Second.Text = i
                wait(1)
                  if Second.Text == "1" then
                   map = game.Lighting:FindFirstChild("MAP1"):clone()
                   map.Parent = game.workspace
                   map:MakeJoints()
                   GUI.Seconds.Text = " "
                   GUI.Title.Text = "Loading Map"
                   wait(7)
                   player.Character.Torso.CFrame = CFrame.new(Vector3.new(967.119, 41.396, -391.16))
                    RoundBegin()
                  end
            end
    end

Although correct me if I'm wrong as I have not tested and not scripted in a while, please excuse me if it is wrong, but if not, I hope it helped.