Six to seven days after the split we need to check all frames in the nucleus for queen cells and remove all queen cells that are already capped, provided some uncapped queen cells with a queen larva inside remain on the frames.
Reason: When we created the split, the bees in the nucleus, being without a queen, panicked and started building so called "emergency queen cells" to raise a new queen. By doing so, they might have built some cells with a larva inside already 2-3 days old, already on its way to become a worker bee. Although a larva raised in this way would still develop into a queen, chances are she will not become a very strong and productive queen as she has been missing out on the protein-rich food a queen larva is being fed throughout her entire development.
Larvae of female worker bees are being fed Royal Jelly for a day and a half, then their diet changes to "bee bread", a mix of honey and pollen, prepared and fed to them by the nurse bees. Larvae of queen bees are being fed Royal Jelly throughout their entire development until the cell is closed 7.5 days after the egg was laid.
If after six to seven days you find a closed queen cell, it means the larva inside is more than 7.5 days old and has already been on her way to becoming a worker bee before the "emergency queen cell" was built for her.
Without intervention by the beekeeper, the first queen emerging from the "emergency queen cells" is the one that has had the least amount of Royal Jelly and is therefore the worst candidate for a good queen. Once emerged, she will kill all the other queens still in their queen cells.
Raising queens by splitting a hive can only produce good quality queens when the weakest candidates are removed before they emerge.
This has to be done exactly six to seven days after the split; if done too early, none of the cells would be closed; if done any later, all queen cells would be capped and there is no way to determine which ones are going to be the better queens.