Hi tung,
I would pick the day, say the first of the month. If you are charging that day, do 100% otherwise do 80%. If the car doesn’t get plugged in that day, then it will miss it. Not a big deal, right? If it is pick 2 days in a month.
I’m sure that can be done. Also having someone or something writing it for you means the second it misbehaves, you will be struggling back to find someone to fix it for you.
The best way to learn is to just try. Run thru the docs on getting started with the automation editor. If you get stuck, come back with what you have done.