Time information in Kinovea is relative to a specific point in the video. By default, this is the start of the video or working zone.
To set the time origin to an arbitrary point in the video navigate to this point and use the Mark current time as time origin button or context menu. All displayed times will be relative to this origin, using negative time before the event and positive time after it.
Setting the time origin to another point of the video can be useful to quickly get timing information in relation to a specific event, for example, a golf ball impact, a pitcher's release point, a long jumper's take-off, a starting gun trigger.
See also: /measurement/time.