When Google's new search options feature went live earlier last month, Google also changed how they handle time based queries.
Back in 2007 Google handled the time based query refinements by appending &as_qdr= to the URL, now Google is using &tbs=qdr: for the same refinement. Let me show you how it works:
To show the pages indexed by Google on this site for the past day, I use the site command and append the past 24 hours refinement.
- Old Way that still works: http://www.google.com/search?q=site:seroundtable.com&as_qdr=d
- New Way: http://www.google.com/search?q=site:seroundtable.com&tbs=qdr:d
So as you can see, both methods still work. Why duplicate the efforts? As Tedster said in a WebmasterWorld thread, it is possible that two different teams at Google worked on the various features and didn't consult each other.
Forum discussion at WebmasterWorld.