The nearest expiration date for Gulf Coast Jet Fuel (Platts) Futures (Aug 2017) is Aug 31, 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 Gulf Coast Jet Fuel (Platts) Futures (Aug 2017) before Aug 31, 2017.