What does the "Add Time" feature do that is located under TOOLS when editing a video?

The Add Time features shifts all elements in the video forward by adding a block of time. The start time marks where the shift will begin, the end time is used to set to amount of time added. For example, to shift all content from 00:00:05:01 on ahead by 5 seconds, set start time to 00:00:05:01 and set end time to 00:00:10:01.  When you add time and click SAVE in the "Add Time" window, an indication of time added will appear in the timeline slider in green as shown in the image below. If you are pleased, close the Add Time window and click SAVE on your main authoring toolbar to save your work.

If you are not happy with your work, simply leave the editor to abandon your changes.