Part of a horses' essential needs is they need to eat 20 hours a day. Horses are not built to eat 2 or 3 times a day. Slow feeders are a great asset if your horse doesn't have access to 24/7 pasture. Below is a 2 day Freedom Feeder. These are what my horses use where I board them and all the horses there love them.! I do not like to advise these be hung on a fence since horses are meant to eat low, as in off the ground. At my barn they are placed in a container, we use a old brussel sprout containers since they have holes at the bottom. There are also Freedom Feeders Full Bale. This feeds a horse for a full 7 days.
There are many scholarly articles on the subject of how long can a horse go without food. I like the below article by Vicki Fowler Veterinary Equine Dental Technician. You may have to copy and paste to read the Facebook post.