When a time change occurs on a NVR it will create a new timeline. The current timeline will be referred to as Overlapped 0, the timeline for the recordings before the most recent time change are on a timeline called Overlapped 1.
This is represented in Wisenet Viewer by a change in the shading of solid green line:
To to toggle between timelines, right click on the timeline and select Overlapped data and then select the appropriate Overlapped timeline: