The nearest expiration date for Singapore Mogas 95 Unleaded (Platts) Futures (Aug 2018) is Sep 5, 2018.
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 Singapore Mogas 95 Unleaded (Platts) Futures (Aug 2018) before Sep 5, 2018.