I don't know if breed-back times are closely related to first-cycle age, but if they are, it could be a double-edged sword if you have bulls around 7 month old heifer calves... Just a thought
I've had many cows breed back after about 3 weeks naturally mated to a bull, don't know how that works with synching and AI though... One of my cows does best breeding back as soon as possible after calving, if you wait 3 months after she calves to expose her to the bull, she doesn't take... I found out with her help that I had a mineral deficiency and I'll see how she does in future years... This year she's due in august, but I'd lay money that by fall time she won't have the smallest calf, which is the reason I'll hold on to her... that and the fact that it may not be her genetic fault for not breeding back. She's one of the heaviest milkers and she depletes her mineral stores as she lactates, hence breeding back well if exposed early, and being all out of gumption to breed back if exposed late