iPhone does indeed post a message of an estimated time that the battery will be charged....IF....you are using Optimized Battery Charging.
For example.....my phone's battery is usually down to 20-25% by the end of the day. I connect the power adapter to the phone and leave it connected all night.....every night.
After a short period.....maybe 30-45 minutes, if I wake the screen, a message will appear that battery charging will be complete by 5 AM, or 6 AM, for example.
Frankly, I pay virtually no attention to this because I know that the battery will be ready to go first thing in the morning, and the phone normally makes it to the next evening before it needs to be charged again.
That's because Optimized Battery Charging charges the battery relatively quickly to 80% and then the battery rests. Over the next 5-6 hours, the battery is very slowly trickle charged up to 100%, or a lower number if you have set the charge limit to a lower number.....(which I do not do, because I want the battery to start at 100% each day).
It normally takes Optimized Battery Charging 7-10 days to learn your routine, so you may not see a message for a week or so if you wake the phone after it has been connected to the power adapter at night.
More info on Optimized Battery Charging here, if you are interested:
About Charge Limit and Optimized Battery Charging on iPhone - Apple Support
