I just noticed that the Supreme Court has updated the electronic docket for Thomas More Law Center v. Obama (No. 11-117). It now states that the United States's brief in opposition to certiorari is due Monday, August 29. Of course, DOJ could always seek an extension. But as of now, that is the date.
After the United States files its BIO, the petitioners can then file a reply. There is no particular due date for that brief, but they will need to file it quickly. Once the BIO is filed, the case gets calendared for conference and the briefs are distributed to the justices' chambers within ten days. If there are no extensions, the petition will be considered at the justices' first conference of the new term, scheduled for the week of September 26.