It should be obvious that you have to rehearse your presentation before you give it. Although, given the fact that I'm often seeing speaker overrun their time slot, I have to wonder if it's really something many speakers do. I get the impression that not rehearsing (at all or earnestly) is the number two reason for going over time (number one would be trying to cram too much content into the presentation).
Assuming you do rehearse: Is there an upper limit to rehearsing? I.e. can you rehearse too much?
