Postprocess the results of a query with date constraints

I create a search set to scan my favourite RSS feeds sites.
How (well, is it possible ?) can I postprocess these results to only keep the ones of, let’s say, the last 48 hours…well to imitate, within DA, what Bloglines does for instance.

The only possibilities at the moment are to sort the results by date or (if it’s a scheduled set) use the “Only new pages” option.