The nearest expiration date for PJM PEPCO Zone Off-Peak Calendar-Month Day-Ahead LMP Futures (Aug 2015) is Aug 1, 2015.
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 PEPCO Zone Off-Peak Calendar-Month Day-Ahead LMP Futures (Aug 2015) before Aug 1, 2015.