So I've been trying to make a clock using a remote event, why wont the script work?

Looks like you're missing an OnClientEvent in your Local Script. Should also rename your event so it's not the same as your function.

Local Script

TimerStart.OnClientEvent:Connect(TimerStart)

Also, specify which client to start the timer. Server Script

TimerStart:FireClient(player)

Here is what you should have:

Local Script

local event = game:GetService("ReplicatedStorage"):WaitForChild("TimerStart")
local time = 0

local function TimerStart()
	print("working2")
	script.Parent.Parent.TextLabel.Text = 0

	for i = 1, 9999 do
	    wait(0.1)
	    time = time + 0.1
	    script.Parent.Parent.TextLabel.Text = tostring(time)
	end
end

event.OnClientEvent:Connect(TimerStart)

Server Script

local TimerStart = Instance.new("RemoteEvent")
    TimerStart.Parent = game.ReplicatedStorage
    TimerStart.Name = "TimerStart"

function onTouch(hit)
	print("working")	
	local player = game.Players:GetPlayerFromCharacter(hit.Parent)
	if player then 
		TimerStart:FireClient(player)
	end	
end

script.Parent.Touched:Connect(onTouch)