Wigwams right with this.
Overnight Ev tariffs are good for Ev charging but the day rate is more expensive than standard during the daylight hours.
I hammer my overnight charging (2 EVs + charge home battery) for 7.5p a kWh, during the day my rate is 39p a kWh.
The higher rate doesn’t impact me though because my solar/battery cover daytime use with any spare solar going into the car.
A Phevs tiny battery on its own wouldn’t justify an overnight tariff.