During the Gettysburg campaign.
True. At Gettysburg he had extended himself beyond where his previously used supply lines could reach. In the context that I was using the term "strengthen his supply lines" a better choice of word would have been "reestablish his supply lines by extending them to Gettysburg."
However, as others have pointed out staying in Gettysburg after a victory was not an option that would be given serious consideration.
An evaluation of the Unions strength (would they have withdrawn to lick their wounds, or surrendered) after a defeat of Meade, would be critical to the decision making process before a next step was to be seriously considered.