Breed Post Ovulation Only
Inseminating within six hours from ovulation is the number one priority for success with frozen semen. The timed protocol may work in some instances, but why inseminate with expensive, no-guarantee frozen semen before the mare ovulates? Mares are known to regress follicles, which means your expensive semen is wasted. And what if the semen only lasts for six hours in the reproductive tract, and your mare ovulates at ten hours post insemination? This is why the veterinarians will put another dose in when she/he checks the mare again, regardless if the mare has ovulated or not.
The main reason veterinarians want to use the timed protocol, which calls for one dose to be inseminated before the mare ovulates and one dose after ovulation, is so they don't have to get up at night and check a mare. There is no reason to use two doses per cycle when one will do. If your vet uses nothing but the timed protocol, I suggest finding one who will inseminate post ovulation.
There are, however, reasons to use the timed protocol, such as when you have a mare or foal you don't want to ship to a breeding facility or you don't have the option of using the post-ov protocol.
I believe the most fertile frozen semen stallions are those whose semen lives the longest in the reproductive tract. I've seen frozen semen that is still alive on a slide after 12 hours, but most lives far less. With stallions that are less fertile, consider asking your vet or tech to shorten up the interval between checks, to inseminate closer to ovulation.
It can't be overstated, inseminating post ovulation is the single most important way to be successful with frozen semen.
Don't Breed on a Transitional Cycle
Even though mares get in foal at the end of a transitional cycle at the same rate as with any other cycle, the fact that transitional cycles can last up to 21 days means it can cost you a fortune in board and veterinary costs. Plus, the transitional cycle gives the mare a cleansing cycle, as nature intended, and gets her hormones working. After the transitional cycle she'll settle into a normal, regular cycle in most cases.
Don't Breed on Foal Heat
Your vet might tell you she/he no problem getting mares in foal on foal heat, which is true enough. But the more important fact is that there is only a 30 to 35% live foal rate from foal heat breedings. I bred on foal heat only once, to save money on very expensive board. The mare came home pregnant, but aborted at nine months. The placenta was horribly infected, as was the mare's uterus. The uterus needs time to cleanse and heal after foaling, that is the purpose of the foal heat. So give your mare's reproductive future a boost by waiting a couple weeks for the first "real" heat.