Office Timeline can accommodate some changes that you make manually on the slide (using PowerPoint’s controls instead of the add-in’s). This post explains how to save those manual changes.
Click on the timeline object you want to modify and make the desired manual change (date & text updates, color adjustments, etc). In our example, we will manually change the highlighted End Date from Sep 7 to Sep 30 by typing in the new date directly on the PowerPoint slide.
Make sure to click the Accept button on the Office Timeline ribbon once you've made your manual edits or customizations.
Office timeline will save all supported manual changes and update your timeline accordingly.