what does the '%' in a string do for time??

local Lighting = Game:GetService('Lighting')


local function GetTime()
	local timeFormat = "%.2d:%.2d:%.2d" -- Right here this thing
	local t = tick()
	return timeFormat:format(math.floor((t/3600)%24), math.floor((t/60)%60), math.floor((t%60)))
end

while true do
	Lighting.TimeOfDay = GetTime();
	wait(1)
end