My vet has said that it should be 63 days from time of the LH surge, which is effectively 61 days from ovulation. My actual experience has been that my dogs have their puppies 59 to 63 days from ovulation.
I had one litter that I did not do any progesterone testing--and I think she was bred too early (the first litter I bred). She had her puppies 66 days after the day of first breeding--and it was a small, 2-pup litter. Another female of mine never went past day 60 and she was regularly progesterone tested to make sure I knew when she was ovulating.
So, really, 59-63 days doesn't help much at all. I watch the female closely and take her temperature twice a day after day 58. If the temperature drops below 99, then usually, serious labor will start within 24 hours. However, since the temperature will "bounce" below 99 and then back up, you can miss this drop.
Behavioral changes have been the biggest indicators for me--panting, agitation, denning, digging mean that pre-labor has started and real labor will start sometime in the next 24 hours.