While the 'usual suspects' battle it out, i'm amazed the posting from ON MARK BOB didn't get more coverage.
I'm afraid Sir, that you are wrong and have been lucky to have not heard further from the regulatory authority.If there was a serious threat to yours or the lives of your pax, such as terrorist attack or tsunami warning, then you would have been justified in exceeding 3 hours. You are correct in that the original duty was not planned as a 3 sector day and that the security alert was unforseen. THAT is why as Commanders we have the right to use discretion to cover such situations, but in any event, should NOT exceed the absolute 3 hours. Regardless of how many sectors were planned, your actual FDP limitations are now governed by the actual number of sectors you do.
Regards
BYMONEK