I HAD 12 chickens and one died (that's another story) and today, with 11 chickens left, I gathered 12 eggs from the nests. How can that be? Can some chickens lay 2 eggs a day? Sure, I COULD have miscounted, but, hey, I thought I did pretty well between one and twelve!
It's been discussed before and anything is possible. However, extremely unlikely. Whenever I thought I had more eggs than chickens, I'm sure I miscounted, failed to see an egg the day before or there was a hen that laid after the last collection the previous day. It takes about 25 hours to make an egg and ovulation doesn't occur till after the last egg is laid. The exception would be a multiple yolk egg. The egg spends most of the time in the shell gland and I don't think it can accommodate 2 at a time. http://www.thepoultrysite.com/publications/1/egg-quality-handbook/2/formation-of-the-egg There are other oddities that have happened like an egg in an egg but those are so rare they don't even know how it happens.
It is possible. I have one pullet who was laying two eggs every other day during her first month of laying; one was always about the size of a walnut and the other a grape. I didn't think it was possible until I separated her to figure out if the double eggs were coming from her or if I had another pullet who always laid on the same days at the same time. It was too much of a coincidence to not wonder. I work from home so frequent nest checking and eventually deciding to separate the pullet until the mystery was solved wasn't an issue. Once her reproductive system sorted itself out she stopped laying the two smaller eggs every other day and laid one larger one each day (until winter hit).
I have seen 2 eggs in one day, especially from very young birds or an older hen that seems to be releasing too many yolks too quickly. I have a BR pullet that started laying at 5 months old. For nearly 2 months after she began laying, she laid a good egg in the nest box in the morning and then that night laid a soft shell off the roost bar. She eventually got her egg laying machine in gear. I also have an older hen that will lay a perfectly good egg in the nest box and will sometimes for weeks on end, lay another egg later that day. Sometimes she will put a good shell on it and sometimes not. Young pullets have to get their system in gear and sometimes older hens that are ending their cycles can send out too many yolks. Too many treats and fat birds will also send out too many yolks during the natural yolk cycle of 25 to 27 hours.
Definitely possible. I had one lay two eggs in a day a couple of times. Mine never got the memo on that whole 25 hours to make an egg thing because I have two that lay at pretty much the same time every day, it doesn't get later and later in the day as the eggs go. 8 am sharp every day I can count on these two having laid their eggs. So, as a rule it doesn't happen but some chickens just don't care about rules