Without knowing anything else, I suspect that you are running
omnirpt -report list_sessions -timeframe [start] [finish]
or the GUI equivalent
You may want to try
omnirpt -report list_sessions -tab -timeframe -24 24 -log C:\temp\sessions.txt
Of course, you can pick any timeframe, and designate the log file in any path that you like. Since the '-tab' argument was used, this report will be tab-delineated, and suitable for import into Excel, and you can see if the End time column exists
If it is not there, then make sure that you are current with your Data Protector patches. Since you mentioned that you are running DP 7, I recommend that you install the patch bundle to upgrade to DP 7.01, along with the current patch set for the Core suite of patches. These are available from the SSO site by click Down-loads -> Software Patches.
If, after all of this, you are still not seeing the End Time column, you will need to open a case wit DP support