There is currently no way to get this relative date range to be in title automatically. However, by creating two calculated fields to find the min and max dates, then placing them on the level of detail shelf will allow them to have a range. I have attached a sample workbook showing this. Hope this helps!
Of course that way only shows the min and max that exist, not the range defined in the filter - which would be really nice to be able to do.
There really needs to be an option to convert a comment in a forum thread into an idea in the ideas area. There, now that's two ideas...