Never, ever, ever, ever overrun. Ever. Aim for 75% of your allotted time, make sure your practise delivers that and ensure you have a means of monitoring your performance on the day. No presentation is made better by going on longer, quite the reverse. Never over run.
Prepare a presentation for 75% of the allocated time. You will KNOW exactly how long your presentation will take because you have practised and achieved that repeatedly, if necessary by editing. All talks take longer on the day, never expect less and never think rushing will help. No audience will complain, no organiser will ask you to fill the space and everyone wins. Aim for 75%.
As well as rigorous practise that has shown your expected time, you must have at least two means of knowing the passage of time. Never think you can over run because the previous speaker’s has done so. Some organisers have a countdown clock on the stage, most presentation software has a set up allowing any combination of elapsed, remaining and current time and you have a mobile phone. It takes little effort to set up a countdown timer with SILENT VIBRATE for your 75% of your 75% time. Press start as you rise from your seat. With your 25% remaining time you can safely relax and rise to the punchline.
It is mandatory that you effectively and clearly deliver the punchline by the allocated time. There is never an excuse for failing even if this requires an artificial break. It is better to arrive and deliver the denouement than rush crazily into it and fail to capture the audience for that last moment. Timing takes practise, not luck. You, your message and your audience deserve it.