C#, wake computer from sleep

I'm creating a small alarm clock for fun, and I want to wake up the computer from sleep at a certain time.

I found this code, http://www.pcreview.co.uk/forums/showpost.php?p=11849260&postcount=4, and it works.
But.. as soon as I initiate it the program becomes unresponsive until the timer is finished.

What to do?

>>2
P/Invoke is for calling native libs. It's basically FFI.