creating a timer?

I have to create a game for one of my classes, and I'm wondering how i can make a timer that counts down from a minute or so.......and then the game ends when the time runs out

1. Look at Chapter 10, example 1 starting on p.252 in the text by Dunn, et al.

2. Do a search of the forum for "timer." There are at least two or three examples that have been posted.

This maybe very crude, but of the four Alice books I have none are Dunn so I created an example that works. If there are more efficient ways to get it done, please share.