You will have to modify your content pdfs (or the feed where
the metadata is coming from) to the 6 digit format YYMMDD.
Once you have done this and recrawled the content (or in case of a
metadata feed re-feed the xml) test on the XML results, that the meta
tag
now has the new format <MT N="ModDate" V="080815"/>.
Once you have made sure this, you can use the daterange query the 6
digits
in your url: inmeta:ModDate:080815..080815.
Cheers
Mike