A web based lightning talk timer available at the following URLs;
You can optionally set the seconds to count down from and warning time in the url.
30 seconds, warning at 15 -- http://lightningtimer.io/#30,15
5 minutes, no warning -- http://lightningtimer.io/#300
After lightningtimer.net, one of the most simple but awesome lightning timer websites, disappear I created a mirror with the same functionality.