FIRST has some power point presentations already prepared. You are welcome to download and adapt for your uses. You could use the global info here and then add info about your team.
http://www.usfirst.org/community/res...er.aspx?id=952
Less is better than more. Allow time for follow-up questions. 15-20 minutes for the presentation is good. [NOTE: this will be hard. It's not much time.]
Be sure to practice in front of people first. Team members and mentors would be great. It seems that people always underestimate how much time they take. Don't just read the slides. They are there as background.
Good luck!