Few broodmare owners have seen a foal born. Most mares foal at night. There are various devices to alert you that a broodmare is nearing foaling. Using these devices, you can still miss the event if you're asleep. Mares foal rapidly, usually within 30 minutes of the onset of hard labor.
Broodmares also have the unusual ability to delay foaling, at least for a short time.
A person entering the stable every hour or two may also be disruptive to a mare. It seems that they just wait until you leave, then lie down and foal. At the next visit mother is munching hay, and the new foal is nursing or sleeping. British researchers studied two breeding farms. Farm A was a Thoroughbred breeding farm where management activities were usually finished about 4 p. m., and rarely later than 5 p. m.