Aberrations can occur. I've heard of a chicken that laid 2 eggs in a day but not every day.
That would require ovulation to take place shortly after the egg enters the shell gland. Normally ovulation isn't until at least 30 minutes after the egg is laid. In high yield hens, normally one yolk is produced on every 24 hour light/dark cycle.
The mechanisms of the initiation of ovulation and oviposition in fowl are well understood.
Science is aware of and has been working to improve upon the physiological block which sets the maximum of one ovulation per 24 hour light-dark period. That limits egg production to a maximum of one a day. This very thing has been studied ad nauseum since at least the 1940s with exhaustive research to try to shorten that, thereby increasing annual egg output.
Imagine what the egg industry would be willing to pay to obtain those genetics if there actually were birds that laid 2 a day. That discovery would be worth millions to the university that produces it and billions to the egg industry.
Upon ovulation, the yolk spends 15 minutes in the infundibulum where it is fertilized if sperm is present.
It then spends 3 hours in the magnum where the inner and outer membrane are added.
Moving on to the isthmus it takes an hour to add the albumen.
Then it goes into the uterus or shell gland where more water is added to the albumen and then the shell is formed and any pigments added. It takes about 21 hours for that process.
So that adds up to over 25 hours. There's no way to speed it up.
It is conceivable that another ovum could be released prior to the egg passing the cloaca but very unlikely. That could possibly be forced briefly with an ahemeral lighting program.
99% of all hens have only one functioning ovary. Perhaps all your hens have 2 ovaries.
Perhaps there are other hens from a neighbor volunteering eggs.
Either that or every avian scientist is wrong.
Edited by ChickenCanoe - 3/10/15 at 2:21am