Start Date On History Alarm Status Table

I can’t seem to figure something out and was wondering if someone could help. I have alarms I am monitoring on a main window with the Alarm Status Table. I was wondering if there is an expression I could use that would make the Start Date to be exactly 6 months from the End date in which I have now() as the expression for the end date. For example if End Date Is 06/09/2014 14:40:53 how I could make the Start Date update Automatically to 01/09/2014 14:40:53. Any help is Appreciated. I have version 7.6.6 of the ignition software. Thanks.

Bind the start date to: