Timer

Hello,
I used to implement timers in AVR and PIC controllers. How to implement those in imp?
I want to set up a timer, I need to perform certain operation for 15 sec. and then need to clear that timer.
Here, I found hardware.millis(); , a free running timer which increments after every milli sec. But how to clear this timer. Is there any other way to make precise use of imp timers? can the logic be implemented without using hardware.millis();?

I think you may be looking for imp.wakeup()

@smittytone wrote a comprehensive article about it here.