Why won't a player teleport when the time expires?

Problem #1:

StarterGui does not actively change anything, it is simply where guis are cloned from, and will not make the changes you need.

To change a player's gui, go to PlayerObject.PlayerGui.

I will rewrite your time script:

for _,v in pairs (game.Players:GetPlayers()) do
	v.PlayerGui.Countdown.Timer.Text = "10"
end
wait(1)
-- repeat

Problem #2:

Your timer script is inefficient, try using a loop:

local num = 10 -- how many seconds
while num > 0 do
	wait(1)
	num = num - 1
end
-- end code

Problem #3:

Not really a problem, but a better way to do your 2nd script will be:

if script.Ended.Value == true then -- create a bool value called 'Ended' inside the script
	teleport() -- to do the equivalent of my answer on Problem #1
end

I recommend you use functions to simplify all of your code, so:

function updateGui()
	-- code
end

function teleport()
	-- code
end

-- etc.

Final Scripts

Script #1:

num = 10

function updateGui()
	for _,v in pairs (game.Players:GetPlayers()) do
		v.PlayerGui.Countdown.Timer.Text = num
	end
end

while num > 0 do
	wait(1)
	updateGui()
end

game.Workspace.Script2.Ended.Value = true

Script #2:

function teleportPlayers()
	for _,v in pairs (game.Players:GetPlayers()) do
		v.Character.Torso.CFrame = CFrame.new(Vector3.new(4, 1, 7))
	end
end

script.Ended.Changed:connect(function()
	if script.Ended.Value == true then
		script.Ended.Value = false
		teleportPlayers()
	end
end

Hope I helped :)

~TDP