Looking for help with a timer

I am trying to figure out how to do something if a monitor hasn't been touched in X mins/seconds. For example a screensaver where if you don't touch the screen for 5 mins then it runs a screensaver program, then as soon as you touch the screen again it pulls back up your program.

Should be farily straightforward using events and the parallel api

local timerId = os.startTimer(300) --start the timer
while true do
  local tEvent = {os.pullEvent()} --get events
  if tEvent[1] == "timer" then
    if tEvent[2] == timerId then --our timer has elapsed
	  parallel.waitForAny( --wait for any of the following functions to finish
	    function()
		  os.pullEvent"monitor_touch" --this function ends if a monitor touch is detected
	    end,
	    function()
		  while true do --never ending
		    --screensaver here
		  end
	    end
	  )
	  timerId = os.startTimer(300) --restart the timer
    end
  else --something other than the timer happened
    timerId = os.starTimer(300) --restart the timer
    --other functionailty here
  end
end

Thank you very much, im planning on using http://pastebin.com/KQjmtASU matrix screensaver then just having a standard program for controlling my auto spawner. Could i just use shell.run("matrix") for the screensaver? then just use error() to quit that program and start my mob spawner program? Or would it be easier to just combine all of that into one program

Throwing shell.run("whatever program") in where it says "–screensaver here" should work just fine. However, im guessing you don't know how the parallel api works, so i suggest atleast having a look at it. It's good to know
http://computercraft.info/wiki/index.php?title=Parallel_%28API%29