The nearest expiration date for Los Angeles CARB Diesel (OPIS) vs. NY Harbor ULSD Futures (Feb 2017) is Feb 28, 2017.
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 Los Angeles CARB Diesel (OPIS) vs. NY Harbor ULSD Futures (Feb 2017) before Feb 28, 2017.