It will ask you what do do; respond with... add (this will add a timer) delete (this will delete a timer) reset [number] (this will reset the specified timer, yes you need a space in between "reset " and the number
Basically how it's done is: resetting a specified timer sets an item in a different list to the actual timer and then it takes the difference. Ehh I'm bad at explaining these things... look inside, it's fairly straight-forward