There is an article back from 2018 that says that most gains for $SPY happen overnight stating that you could have done overnight hold since 1993 and be more profitable than running the same by marker hours.

I thought why not to review this thesis in a bit more detailed way. I set a simple backtest that is not going back to 1993 but rather just to Jan 1, 2010, holds overnight and sells in the morning.

Below are the result of backtesting with http://breakingequity.com/