The nearest expiration date for PJM AECO Zone Peak Calendar-Month Day-Ahead LMP Futures (Jun 2013) is Jun 29, 2013.
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 AECO Zone Peak Calendar-Month Day-Ahead LMP Futures (Jun 2013) before Jun 29, 2013.