I don't know the usual turnaround on an en banc hearing. It varies.
Amarin's case is very dependent upon GSK v. Teva. Reversal would be a crushing blow for Amarin's infringement case. Perhaps not fatal, but a likely setback. The case would not be mentioned in the Complaint, where cases are usually not cited. You can bet though, that the case will be heavily relied upon in any injunction or summary judgment Briefs.