Hi! Some people have good luck with pullet eggs but that is not my experience.
My experience has been that pullet eggs can grow and hatch, then be non-thrifty chicks and die soon after hatching.
Example: I moved 2 cuckoo Cochin pullets in my Frizz pen so they could be mated with the roo there. Both were new layers, one had been laying a week and the other just had laid a couple of eggs. I wanted to get cuckoo / blue cuckoo Cochin chicks, NOW.
I set all their eggs after they were with the roo and they were all fertile and hatched. Sadly, the chicks from those cuckoo pullets lived a few days and all died. Nothing wrong with them I could see, just not thrifty.
I had the same thing happen when I got my first Silkies and got over-anxious when they started laying.
Sometimes 'pullet eggs' are do-able, and sometimes they aren't.
I should have learned my lesson when that happened the first time.
This time, these pullet girls had been dosed w/ vitamins & electrolytes and had been getting extra protein (boiled eggs) and it didn't make a bit of difference in the outcome of the hatchlings.
The best that can happen is you get new chicks from pullet eggs. The worst that can happen is they hatch and die.
My overall experience has been that it is better to wait at least a few weeks / month before setting a particular pullets eggs.
Good luck!
Lisa