Time lock

while true do
    local event,param1 = os.pullEvent()
    if event=="redstone" then
        if rs.getInput("front") then
            timerID=os.startTimer(300)
        else
            rs.setOutput("back",false)
            timerID=nil
        end
    elseif event=="timer" and param1==timerID then
        rs.setOutput("back",true)
    end
end