This site provide useful countdown and stopwatch that mark important event. Also offers self countdown and stopwatch in dedicate section. Here below there is one example:
This is a Time CountDown. The forms are setted with hours, minutes, seconds and the date of the your pc. Put in forms the data of your exact moment and it will count the time gap.
This is easy online stopwatch. Push START and the counter will start. Yuo can also get several split time. Push STOP and RESET and the the stopwatch will able to restart.