Optimised Battery Charging charges my iPhone hours before I wake up

I have optimized battery charging turned on and an alarm for 6 AM every morning. I wake up at the same time. However, the phone finishes charging at 4:30 AM itself for some reason. I don't understand why and wonder if it's overcharging between 4:30 AM and 6 AM?

PS: I don't wake up in the middle of the night to check my phone or anything.

I have a newly replaced battery and don't want to ruin its health so if anyone could help me understand this process.