The nearest expiration date for Brent Crude Oil vs. Dubai Crude Oil (Platts) Futures (Jan 2016) is Jan 29, 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 Brent Crude Oil vs. Dubai Crude Oil (Platts) Futures (Jan 2016) before Jan 29, 2016.