The on-time annotation will automatically perform an action when a viewer reaches a point in the video without the need for a click from the viewer.
Add an the annotation with this icon.
You then add the event you would like to happen when the viewer reaches that point in the video. The most common events are...
Pause the Video
Play the Video
Jump to a Time in the Video
In the Jump to video time field select the chapter you'd like to jump to enter a Custom time.
Here are details on advanced uses of the On-Time annotation (like Addon Type and Command.
Note: By design, the on-time annotation does not perform its intended functionality while in edit mode. This is to avoid disrupting the editing flow. To test, switch to view mode (or "show" mode).