Big question would be what do you do with these cows, and how are they producing milk-wise? If they're really heavy milkers and they're in a dairy herd/going to be at a dairy you'd want to wait longer to breed them back; no sense in being forced to dry them off when they're still milking upwards of 60-70lbs per day.
If they're just milking so-so, and you're only raising calves on them, you may want to breed them back sooner...or not. It's really all dependent on what you want and what you're doing with these cows. If they don't hold their milk well and don't milk that great you'll want to breed them back right away so you're not dealing with them not producing enough to pay their keep, and not being close enough to calving to dry off.
I've seen some that bred back around 10 days post calving, but most the earliest you can breed back is 30 days post calving, and they won't always take the first time they cycle/first time they're bred.
Hope that helps.