The nearest expiration date for E-mini S&P 500 Futures (Dec 2016) is Dec 16, 2016.
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 E-mini S&P 500 Futures (Dec 2016) before Dec 16, 2016.