Could someone help me out on why this countdown from 300 to zero won't work?

When I click a button in my game's workspace, I made it set a value to 300 (this works fine) however the countdown script that I put inside the value does not work and I can't understand why. I want it to countdown from whatever number it is at until it is 0. I have tried repeat until the value equals 0 and the countdown just keeps going.

while true do
	if script.Parent.Value > 0 then
		script.Parent.Value = script.Parent.Value - 1
		wait(1)
	end
end