Buy The Close
In my experience, markets sometimes open up with a pump in prices. In situations where I bought near to the open because of some anticipated event, I usually bought at a higher price than if I had waited.
I find it's best to watch stocks throughout the trading day, then put in a buy order in the final hours or minutes before the market closes for the day. This is general knowledge for most investors and traders. While not always a certainty, I think it is a good tip to keep in mind when adding to your portfolio on any given day.
Buy the close, because "gains happen overnight": https://breakingequity.com/blog/most-gains-for-spy-happen-overnight-a-quantitative-study