Can anyone tell me what happens behind the scenes in the timer control? How many cycles does it steal and how often?

I am considering using a timer to detect a change in status between apps. I want to detect at about a 2 second interval so I only need to run a few lines of code every 2 seconds. My concern is how much this approach will affect other processing. What is happening within the timer itself. For instance - does it run code every millisecond? And if so - how much?

Thanks much,
Nancy