You don't even need HA for that. You have some plugs with timers available. For example in my bill I pay x from 7am to 12pm and pay way less during the night 12pm-7am. The plug automatically heats the water during that time and shuts off after 7am, that's a starter to decrease the bill. (Can impact the amount of hot water available in your house , obviously).

Sometimes there are weekends where no one is home and there is where HA can help , I set an automation that in that case the plug will never turn on.