Hi BFL13,
My water heater testing showed that time between cycles was about 4 hours, and that cycle time was 15 minutes if no water was drawn. That was with a 1400 watt element in a 10 gallon US water heater with the ambient temperature at 18 C.
With 810 watts of solar, I'd have no qualms with running the water heater at night via the inverter. Worst case it would draw about 1 kwh. That should yield a nice moderate cycling of the battery bank.
During the day I'd move the fridge to electric, too.