That's how a lame duck was defined during the Clinton Presidency from my recollection. If you stretch the definition you might go so far as '07 when primaries heat up. I don't recall it being from the minute someone is electd to a 2nd term, but imo, it's more wishful thought on the part of the Press as well as a desire for a story.
I saw 1 or 2 commentators call Clinton a lame duck shortly after re-election, not many but it did happen. It irritated me then to, it's the devaluing of the term more than the insult to the man that gets me (never had a problem with them insulting Clinton, and I've grown used to them insulting Bush). I think they're trying to change the concept of the second term, traditionally that's when a president really gets to push his policy whether popular or not, opinion polls no longer hold any threat to a second term president so political compromise becomes less important and a president gets stronger; I think they're trying to weaken it, probably because a president that doesn't have to campaign anymore is a president that doesn't need the press anymore so they're trying to re-establish their own importance.
The lame duck period can be stretched if nobody is listening to the president any more, i.e. he has no political power left. That obviously isn't happening in this case.