Mole;

ya, a timer is what you need man, you can find them at every hardware store, and even most chain stores that carry household items. They cost around $6.00 American.. so not sure what that would be in the UK.

1 problem by switching the times like that, is you can confuse your plant and make it wanna go back to veg state (I had that experience once yrs ago)
it just gives stretchy nugs and totally F*'s your flower cycle.

best of luck man!