Can I boil a full chicken for several hours?
After maybe 45 minutes to an hour, the chicken will be very soft and falling off the bones, the broth will have a strong but pleasant chicken flavor, and the lemons and vegetables will probably be completely depleted and disintegrated.  This is usually a good start for home made chicken soup. At this point you'd probably strain it, let it cool, remove the meat from the bones and be left with soup.

After 3 hours the chicken meat will start to get mushy and disintegrate, the cartilage and connective tissue of the bones will also be melting and releasing gelatin into the broth, the vegetables will also disintegrate.  This would result in a pretty strong chicken broth that is full of gelatin, which would be good once you strained everything else out.

If you did not remove the fat and skin from the chicken, the will mostly melt and leave rendered fat in the broth, but some of the skin will never melt and will remain with a very unappealing texture and flavor.  The fat will generally float to the top and can be pretty easily removed once the broth cools.