But the futures charts the next morning will reflect the effect of the extended session. Imagine 20EMA on 5 min at 9:30am
What you are saying will certainly reflect (extending trading session effect) in cash charts which can't grab the move after 3:30. I am eager to see the volatility in the morning due to the matching of spot and future prices in the morning for individual stocks.
Lots of market has lunch break. You can call it here snacks break. You can't call it a lunch/dinner break.
https://en.wikipedia.org/wiki/List_of_stock_exchange_trading_hours