I thought it was a difference in (adult) breed size. The Dutch chicks I had last year were much much smaller than the bantam Sussex. The Vorwerk were in between. They hatched within 2-3 days.I've been asking myself that very question! That's the problem with buying chickens, there's no guarantee of precise age.
Dutch and Vorwerk. Adult Dutch are around 500 grams. Vorwerk 700. Sussex 800-900, but they seem to grow slower because there was no size difference with the Vorwerk.
July 2023 Vorwerk an Dutch
June 2023 all chicks with their adotive mothers.