DON'T freak but mares can have 15 minute labor to delivery and they don't wait for you to check on them. Some stories sound like horror tales but end fine, like the local mare who foaled in the middle of the night in the pouring down rain and sloppy mud. Healthy mare, healthy foal.
Care exclusively for your mare. She is more important. Sometimes a foal doesn't make it. That happened to Zenyatta, who miscarried 1x. Perhaps a good outside dog and a cow bell for her to wear? Many breeders install a webcam and keep a halter on with a chip with an alarm that will go off every time she lies down. For years, many big time breeders have kept staff who live in the stall next to the ready to drop mares.
Educate yourself so you won't be surprised. Make sure that your Vet has or has access to colostrum milk for orphaned foals. They can only get antibodies from the mare in the first 24 hours. After that you can lose the foal, too. Usually they milk donor mares.
It's a new phenomenon, but some breeders impregnate surrogate mares with fertilized eggs today to keep their champion mares showing, but to also breed and register their foals.
When I learned about these things, it turned me off to breeding. Cattle breed and give birth easier than horses. But, you're committed. Looking forward to a January foal!!