Heads up if you don't already know. Beginning Sept 5, 2017 US security transactions will move from T+3 trade settlement to T+2 (ie settles in 2 days rather than 3). See
This won't impact any backtesting or the Q contest (which never incorporated any settlement issues). This probably won't impact anyone trading in a margin account or even Robinhood accounts. However, it may impact any cash account trading.