Hi,
It takes 90 minutes for my ten gallon water heater to cycle. It draws 1200 watts. If no water is used in four hours it will heat again and takes 15 minutes to cycle. So if you are paying for electricity or gas it is best to warm it up, then shut it down until the next use. I find that running it first thing in the morning works well for my camping lifestyle.
The savings are 1.8 kwh per day.
When I was part time I'd use the water heater to deliberately discharge the battery bank so that my solar harvest would not go to waste. Now that I'm full time, I do not have that luxury.
