Improvising to adjust to unexpected disruptions may include changing from a small group exploratory (learn as you go) activity to a more directed practice or demonstration/lecture.

In my experience, the most common time management problem is that participants have difficulty arriving on time each day due to unreliable public transportation. So then we have to decide whether we’ll start on time and find a way to catch up those who arrive late or if we’ll start and end later as a whole. If we’re starting later than planned we can offer to those who have already arrived additional learning opportunities, such as review of prior concepts, a little quiz, practicing something, etc. Or, they may prefer to use that time to take care of personal tasks.

Have a timekeeper which the presenter has chosen himself give the yellow and red card signal. Yellow card to show that you are coming close to the time deadline and the red card to signal that it is now time to give the closing statement or sentence.
Keep your alarm in your cellphone in your pocket with no sound but vibration mode to remind you that you approaching the deadline

Practice your sessions/presentations so you have a decent idea of how long they will take. Be firm when addressing participants who get ‘off track’.

In planning the presentation, identify on your notes items or examples that should be eliminated if the time doesn’t allow,and then skip over them when the time is running late.

Similarly, breaking into small groups takes time, so an alternate activity where the same information may be shared in an observation session with a sharing of discussion with the person sitting right next to you would save time.

The alert sound in mobile is also great. I regularly set them to use as a real ringtone