[Plantoid]

TLC electrical wholesalers have a 12 volt time clock / switch in ther equipment range.
 
I think it is programmable for several events per day and think it can switch up to 10 amps. Cost was £29 less + VAT

[chrismahon]

I hunted for ages to get a 12V timer switch to give the hens some extra light in Winter Plantoid. Cost £47 inc delivery about 4 years ago. Excellent unit in a fully sealed box and an internal battery which kept the clock going for weeks after I removed the external battery. Bought it from a chicken equipment supplier and I can't remember which one. Only problem I had was red mite getting behind it so I ended up sealing it to the coop wall with Silicone.
 
After a year or so we stopped putting the light on, as the cost of the replacement bedding and extra feed was the same as the value of the eggs. They used to make a real mess in the coop in the few hours before they were let out.