I need some help with a program I'm making. It's a program that will shut down your computer when a download is finished. It's going to be simple, all you do is write the download time in a box and when it counts down to 0 the computer will shut down, but since the download speed will go up and down it will add 30 minutes to the specified time.

All I need help with is how to make the timer and counter, how to make them work with the textbox. So when someone writes a number it will count down when he press "Start".