There are two primary reasons why the speaker may find him or herself running out of time:
or it may be a combination of these factors. Regardless of the cause, it is the responsibility of the speaker to conclude in a timely basis. It is even more important for the speaker to conclude when the next scheduled event is lunch.
If the structure of a presentation is well organized, this will imply at least one of two critical features which will allow the speaker to conclude in a timely manner:
Given either of these pre-conditions, the speaker will be able to summarize in a timely manner. In the first case, the speaker could make a statement such as "While time does not permit me to go into detail, I would like to draw your attention to these three additional factors:" and then simply list those factors, concluding with "Anyone interested in additional details is welcome to talk to me afterward or see my references.". In the second, scalability will allow the speaker to summarize sub-points as opposed to going into more significant detail. In general, to keep a balance within the talk, if all major points have approximately equal weight, it would be more useful for the speaker to recognize as early into the presentation that summaries will be required and thereby summarize all tertiary points in the last two primary points as opposed to being required to summarize the secondary points of the last primary point. This last scenario will make the presentation appear to be off-balanced.
However the speaker finishes, he or she should not make the audience believe the speaker is being rushed. If time is running out, the speaker should not continuously look at his or her watch nor should they suggest that they are pressed for time. This will focus the audience on the time factor and distract them from the discussion.