Some of the early sites that experimented with this kind of change in response to Panda saw improvements begin within a months or so. That still might not be enough for you to receive the kind of traffic boost you are talking about in time for holiday sales.
Remember, Panda algorithm scores are not completely integrated with regular scoring on a daily basis the way things like PageRank can be. So even if you make all the nest changes you can, it still takes a Panda "data refresh" at least - if not a full update - to see the effect of the changes in your rankings. Adn the most recent update was November 6, so I would make changes ASAP if you hope to see any benefit for the holidays.