How to add time to a timer?

Is there any way to add time to a timer? It is very very necessary for something that I am working to to be able to add time to a timer, because when I just call multiple timers, everything gets a bit weird. Can anyone help?

You could either destroy the old timer, and recreate a new timer with the added amount, or use a lua timer library and add it your own way: http://pastebin.com/Gp3LKw1P

4th parameter will be optional in next update.