You can trade ETF's until 4:15pm, but the volume drops off and the spreads sometimes even on the SPY can be .05 or more. But, it is a great way to play ES/VIX futures after the market closes.
One way I was looking at benefiting from the QQQ 4:15pm cut-off time for options was during earnings - especially AAPL, since they were so heavily waited on the QQQ. Most post-market earnings move appear to happen within minutes after 4:00, and that move carries on to the next day on stocks like FB, AMZN, AAPL, MSFT taking the QQQ with it. So you buy QQQ calls or puts depending on the move between 4:00 and 4:15pm.
BUT ........ AAPL reports well after 4:15pm, so that eliminates AAPL. And you do need the market to carry on its momentum the following day.
