Clarification - the format of the poster session is like this:

You put up your poster on the wall (and the other 4 groups do the same), then you stand by your poster and anyone interested in it could ask questions, discuss the methods and results on the poster. This "anyone" could be your fellow students, your teachers at this course, and maybe a couple other interested people here at SciLife.

Consequently, you don't stand by your poster all the time, since you also need to look at the other posters. At scientific conferences, a poster session is usually "mingle time" where you walk around and talk science to the poster presenters and other people you meet there.

Thus, there is no specific time allocated to the presentation of your project. There will be no specific time where you get everybody's attention. You should not prepare a powerpoint presentation - only a poster!