In the morning so that they are not caught off the roost when the light suddenly goes out. I plan to have my light kick on at 5am and off once the sun comes up with a timer. That way they just have the gradual sunset like normal but should give them 12 hours of light.
12 hrs day. The idea is have them up and feed so they can lay. I found that dusk light does not benefit since they would roost at sunset. The light would be on and they just sat at their roost wondering why the sunset was extra long. Dawn light would get them off the roost and start feeding.
This may be redundant to mention but the light should be turned off when the sun is up, so we are talking about only a few hours each day. I use a 25w bulb because my coop is compact.
You don't have to light 14 hours unless your coop is windowless. Just add the additional hours to make 14. Even so, 14 hours with a 40 watt bulb would be 7 cents a day IF your price per killowatt is as high as 13 cents. 30 days of that would be $2.18! Not really much in the scheme of things.