I didn't think there was any difference in the price of electricity, day to night unless you have an off-peak tariff. My last house had off-peak heating and water heating but you had to be connected to that circuit to benefit and you had no control over when it came on. You could put a socket into the off-peak circuit and charge from there overnight.
Now I have a Smart Meter, but as far as I am aware, all my usage is charged at the same rate, day or night.