Analog clock with Chart

Hello everyone, my name is Maurice and I have a question for you; My problem is this: on an Excel sheet with Microsoft office 2007, I set up an analog clock using a Chart.
After that instead of numbers to indicate the hours and minutes, I chose to insert little squares.
Now I wish to each end of the five minutes, the box will Highlight red or yellow, you have any idea what could be done to solve this problem.
Thanks in advance for any help you can give me. Greetings from a. Maurizio

(PS) send test Project