The bees will generally prefer to use young larvae to start queen cells if there are any available, but to be safe, figure that they can use 3 day old larvae to to start queen cells on the day you split, meaning that it hs been 6 (or even 6-1/2) days since the eggs were layed. Cells will hatch 15-17 days from being layed, so as early as 9 days from when you split. You split on May 23rd, so cells could hatch as early as June 1st (yesterday - which it sounds llike they did
I generally move my cells 1 or 2 days before this worst-case (best case:scratch
-fafrd