15-18 yo students, because they need some thoughts and skills they don't have before.
Time is a big issue. I could give them 4 hours to prepare. I think that's enough and they can finish it as homework (if you let them 10 to 15 days more).
Presentation is between 2 and 3 hours. I did it once as a conference this year and it works. The work was on the european enlargement
click hereIf not the risk is to bother them.
If you think in a different way please tell.
Jean Philippe