Provided you have a reasonable size cylinder with foam insulation (not a loose jacket), you can go a long time before it needs to be reheated.
You have to set the times according to when you use the most water, i.e baths and showers. If you have them in the morning, set the hot water to come on an hour before the central heating and go off half an hour after the last person has finished. This should then provide enough hot water for the rest of the day, though you may need to top it up for an hour in the evening. Again, this will depend on usage during the day.
If you have a washing machine or dishwasher, make sure they are using cold fill only. You can convert hot and cold fill machines to cold fill by using a Y-adapter from B&Q etc. This enables both hoses to be connected to the cold water supply.
