What the electricity you use costs per month and per year.
A bill has three parts: the price of energy per kilowatt-hour, the distribution service with its variable and fixed components, and value added tax. The advertised tariff covers only the first part, so the final cost per kilowatt-hour is always higher.
Divide the bill total by the kilowatt-hours used. That figure includes the fixed distribution charge, so it is far higher at low consumption: at 100 kilowatt-hours a month the fixed part can double the price, while at 500 it barely shows.
Only if a real share of your use can move to the night — washing machine, dishwasher, car charging or a water heater on a timer. If night use is under a third, the higher daytime price usually swallows the whole benefit.
A two-room flat with a gas hob usually uses 150–250 kilowatt-hours a month, a house with an electric water heater 400–700, and a house on electric heating can pass 2,000 in winter. Always compare over a full year, since winter and summer differ several times over.