Back in February my wife and I bought four Barred Rock, two Rhode Island Red, two Red Leghorn, and two Cornish Rock hens back in February with two RIR Roos (which I kind of think was a mistake). Our Leghorns started laying by the end of May and by mid-June we were pulling eight to ten eggs a day from our nesting boxes.
We put all the hens on layer feed as soon as we started getting eggs. The only glitch we had was when they started laying in a hay bale I'd placed in the coop to keep it out of the rainy summer weather instead of the nesting boxes. Now I check both the boxes and the bale because there will be eggs there.
We have four Easter Eggers and nine Silver and Gold-laced Wyandottes with a Buff Orpington, White Rock, and Mixed Wyandotte born on June 1, they are isolated from the "big girls" and the roos until they grow a bit more, but I wouldn't be surprised to find an egg out there when I go check on them any day now. But I wonder whether having roos with my first batch might have sped up the process of egg production?