I usually do the the twelve hours but someone around here does over 500 and they stop 48 hours before. He pulls the feed the two nights before he butchers. I feed mine the morning before and that is it. I keep them locked up so they can't get anyting the next morning. I have to catch the girls (laying hens) and let them out since I raise them all together.
I usually pull it the night before and leave water. This will get everything out of their system except the gizzard. I don't really care that the gizzard is full of corn so I don't bother pulling feed for any longer.
It really helps to have them in a small cage so you don't have to chase them around to catch them for processing. I have a collection of wire rabbit cages I put them in the night before I butcher them. I give them little water dishes there but no food, and make sure they can't even reach grass or leaves through the wire.
It's so much easier to catch them at night. Sometimes I'll cage them 2 nights before, give them a little food first thing in the morning, then take it away by afternoon, 18-24 hours before butchering the next day.
It makes their crops empty and most of their intestines too. Besides, I'm so cheap, why give them food that they won't have time to convert into meat?