Here is a link to a User Manual for your softener valve: http://www.wahlwater.com/images/stories/460manual.pdf
Softeners are generally programmed to regenerate when there is little or no water requirements which for most residential applications, is during the night when the residents are sleeping. Unless you sleep during the day due to shift work, it is best to regenerate starting at about 2am as it should be finished regenerating before most people awaken.
As its in the attic I have an overflow pipe installed- only problem it is spilling a huge amount of water(circa 250 litres of water) during the cycle - not sure if it's from the waste pipe or overflow yet?
When you say 'overflow', I expect you are referring to a drain line. When you say 'spilling', I expect you are referring to the water going to the drain as opposed to being spilled onto the floor.
Whenever the softener initiates a regeneration, water is used to loosen the resin and flush out debris, draw brine into the resin, rinse the brine from the resin and then fast rinse the resin to pack it tightly to ensure adequate contact of water to resin during water use. In addition, a volume of water flows into the brine tank to prepare brine for the next regen cycle. Regeneration occurs on a regular cycle, so the water used to regenerate is intended to be flushed to drain.
Concerned about the huge volume of water going to waste.
You are considering the water used to regenerate as 'waste' but it is not wasted as that volume of water is required to keep the softener functioning properly, to provide continuous soft water to you and your family throughout your normal day/week. Water, salt and a little electricity is what is consumed for the softener to function just as fuel and oil are consumed to operate your car and water, detergent and bleach are consumed to clean your clothes.
I don't know how you determined 250 Litres are being used. That volume equates to approx. 66 US Gallons which is probably the correct amount for a residential softener, depending on the softener capacity.
You didn't indicate the capacity of the softener but if you state that info along with the current program settings, the hardness, iron and manganese content of your water and the number of people living in your home, you will likely receive suggestions on the most efficient settings for your unit and water requirements.