The importance of proper rehearsal cannot be emphasized enough. Record yourself during practice and don't stop until you would be comfortable with uploading the result to Youtube. With enough practice, you can be confident that you will be within the time limit. Once you know what to say without thinking, you can also focus on other aspects of your presentation, like making eye contact with your audience, good posture or avoiding fill words like er, um, etc.
Also, never rely on the internet connection at the venue and bring adapters if you have a Mac.