I think what you're looking at is your supplier's off-peak time switch. Eddie 51's right in one respect, they are used for switching on night storage heaters and heating hot water cylinders. However, the times are set and the clocks are sealed by the supplier and if your's has 3 on and off levers it's known in the trade as OP3. What you'll have is an overnight period, usually 8.5 hours commencing around 10pm to midnight, then a mid afternoon followed by an early evening boost. If you have the modern slimline storage heaters, contact your supplier and ask them to transfer you to Economy 7 as these slim heaters do not require additional boosts during the day to work efficiently.