You are quoting from the rules applicable to appellate courts generally but it seems that the federal circuit has its own rules and that the time for file for panel review is within 30 days of entry of judgment under those rules. See rule 40(e) of the attached on page 80, which lists both the general rule and the federal circuit rule. I don't understand why the 14 in the general rule is stricken.
However, the date of the decision is August 3 and the petition was filed on September 4 -- from the docket, which is the 32nd day. It may be that while the decision was dated Friday August 3, the entry of judgment was not until the following Monday or later.
I find it hard to believe that with multiple teams of litigators working on this, they would file a couple of days late, especially where the petition for rehearing was being discussed from day 1. So I expect there is a technical reason, possibly along the lines of my entry of judgment explanation.
9/4/2012 Entry 67 : Appellee [Momenta Pharmaceuticals, Inc. ]-Petition for Rehearing En Banc. Mail Service-9/4/2012. Filed: 9/4/2012. Response requested from: Appellants (Amphastar Pharmaceuticals, Inc., et al.). Response due: 9/24/2012.