The nearest expiration date for PJM PPL Zone Off-Peak Calendar-Month Day-Ahead LMP Futures (Dec 2013) is Jan 1, 2014.
The best time to sell a futures contract is when you've already made money on the investment, but still have plenty of time left before the expiration date. Thus, a good option would be to sell PJM PPL Zone Off-Peak Calendar-Month Day-Ahead LMP Futures (Dec 2013) before Jan 1, 2014.