The nearest expiration date for Singapore Gasoil (Platts) vs. Low Sulphur Gasoil Futures (Jan 2014) is Jan 30, 2014.
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 Gasoil (Platts) vs. Low Sulphur Gasoil Futures (Jan 2014) before Jan 30, 2014.