The nearest expiration date for Argus LLS vs. WTI (Argus) Trade Month Futures (Sep 2017) is Aug 29, 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 Argus LLS vs. WTI (Argus) Trade Month Futures (Sep 2017) before Aug 29, 2017.