The Session Logviewer is a tool to review the history of backup and restore sessions.
The session log is a detailed report of all steps the VSS Writer has performed during the backup or during a restore.
You can also monitor running sessions.
For running sessions the duration of each step is estimated. When the session or the currently executed step is finished the actual duration may change.
Wait steps shown in the session log are used to indicate that the VSS Writer has waited for the next VSS backup/restore event. The VSS events are send by the Windows VSS Service and are initiated by the backup tool. Please also see your backup tool logs to understand why the VSS Writer is waiting.