I heard that turning off the water heater overnight can save up to 30% on electric charges. We do that and turn it on for a while later in the day. Supposedly it only takes 15 minutes to heat up prior to using hot water.

Anytime something can be shut off, esp something like a water heater that runs automatically, there is a savings.

A 7 day programmable 240 volt time clock can be inserted into the circuit to control a water heater.

This will allow the heater to be shut off when no one is home and/or at night. Have the timer come on about a half hour before you would usually get up.

A 7 day clock will allow you to program weekends different assuming there is someone home.

The water in the tank will cool down a bit, depending on the efficiency of the tank insulation, the tank will heat up in about a half hour, to be safe.

You can do this manualy by shutting of the circuit breaker, you just need to remember to turn it back on when needed.

40 gallon tank, no more? What is the ambient temperature? There are times it makes sense, but not always. If you are in FL I would say that it would make sense. You could even experiment with turning it off after use in the morning to see how much you have in the evening.

I can run my boiler (oil, tankless hot water) for 2 minutes, take a 10 minute shower, turn off the boiler, and have enough for dishes or a laundry. That's in the summer, in the north.