BAQ Report Def, default dates?

Using Vantage 8.03.409C, I have a BAQ Report Def where I'd like the user to have default dates show up in the date range fields e.g. Start Date: a year ago from today for the report.

This is an Option Field in the BAQ report designer based on a user defined table's column from the database. I see a column for 'Default' on the 'Option Fields' screen but it doesn't seem to work for me.

Just don't know where and what, I would code for this field?
Please advise.
Thanks in advance.