My marans hen finally started laying about a week ago... at 40 week old! They are all on their own schedules. I have one backyard mix from my august hatch that looks like she could start laying any day... but the pullets from my July hatch look like they are still weeks or months from laying.
When I had Marans they took forever to start laying. Didn't really figure it up but I would say that it was about that long for mine.