I picked up my iPhone 11 Max Pro on launch day. Last night when I plugged it in for charging, the Optimizing Battery Charging notification appeared for the first time. In my case, it took 16 days for the phone to learn enough to start using the feature. The message said it would resume charging at 4:30 am although my usual time to remove from the charger is closer to 7 am. Will be interesting to see if it adjusts over time to more closely align with how I use the phone.