5/ Meanwhile, today we updated the “Show the best Tweets first” setting. When off, you’ll only see Tweets from people you follow in reverse chronological order. Previously when turned off, you’d also see “In case you missed it” and recommended Tweets from people you don’t follow.
It didn't have the actual effect until yesterday or so. It presents your timeline chronologically. Theoretically, you can scroll through your timeline to the last tweet you saw the last time you were on twitter. Twitter used to be like this.
Maybe you always had twitter classic? I'm sure they had to test it.
When I open twitter in the morning, or after a few hours, it will show me a couple tweets, never "just tweeted," but more popular ones. Then I got "in case you missed it" tweets, Never chronological.