@ryanarobson thank you so much for the informative answer! Sadly I can't control anything to do with him right now because I moved barns ( very long story), but I'm planning on buying him within the next year and it's good to know what I should be on the lookout for beforehand.
In my opinion, unless the horse has some sort of dietary restriction, they should have as much hay as they want when they're stalled, preferably in a hay net or some sort of slow feeder. Horses are designed to eat small amounts constantly and feeding 2-3 "meals" of hay and grain a day and then making the horse wait hours for the next feeding of hay can cause all kinds of issues, from simple digestive imbalances to ulcers to colic, and more. The science: horses are always producing bile (which is used in digestion and fermentation) and delivering it to the small intestine, regardless of whether there's food there or not. Stomach acid is also constantly produced- again, regardless of whether or not there's food in the stomach. As well as that, most of a horse's energy comes from fermenting forage in the hindgut. So yes, always having hay available is a must, and if you can use a hay net, that's even better. (I like hay nets because they promote slow, steady eating, proper salivation, and even wear on the incisiors, and reduce boredom and hay waste)