The nearest expiration date for ERCOT North 345 kV Hub 5 MW Off-Peak Futures (Dec 2012) is Dec 31, 2012.
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 ERCOT North 345 kV Hub 5 MW Off-Peak Futures (Dec 2012) before Dec 31, 2012.