As more folks take advantage of this edge, it seems to be a little front running in the last 15 minutes of the cash close.
Its a complete wast of time trying to capture these micro moves during the US cash session.
Buy the U.S cash close....go to bed and watch the index futures float higher. When the U.S cash markets open. Take your profits and walk away. You can during the last days of December, just sit on your gains. Chances of a big selloff are very unlikely.
Do whats best for you, but don't be afraid to hold long overnight.