I think there are logistics that have to be applied if you are inquiring about a boarding facility verses horses who are cared for at a private farm. I also think horses who are traveling a lot & being competed heavily & regularly are in their own category.
In my opinion, I have gathered that the general consensus is this: For horses who have a fairly low key life or schedule, a variance in feed times is healthier as it does not trigger anxiety in the horses over anticipated feed times. For horses with intense & constantly changing competition & traveling schedules, a set feeding time can become one of the few stable & regular activities in their lives that create an opportunity for regularity in their ever-changing schedule.
I keep my horses at home & prefer feeding in a set window of times rather than exact feeding times.
My horses have free choice hay (& seasonal grass) provided 24/7/365 days a year. Stall doors are left open with access to fields 24/7/(nearly)365. They really are only locked in if there is lightening present or predicted.
This schedule works for the horses beautifully, & gives me some flexibility with my work schedule which varies greatly from day to day. This schedule also seems to make things easier on my farm sitters when I need to travel. Most importantly, it keeps my horses calm & flexible about feeding times.
That being said, when I used to board, I think the situation was very different because with the exception of the last place I boarded my horses at, NONE of the boarding stables were willing to provide free choice hay 24/7. So my horses were standing without food for portions of each day & night and they were legitimately hungry at feeding times. This gave them anxiety & created, at times, digestive issues. Plus, when I was driving to the barn during a window of time that I anticipated being able to work my horses, it was a little inconvenient if the horses were being fed at a different time than I expected. Ultimately, your question is about seeking opinions in what benefits the horse the most, so I guess convenience for planned rides shouldn’t really enter the equation. I have found that my horses truly do not care if they are being asked to work during a feeding time now that they are kept at home (even if we are away at a show or clinic), but when they were boarded & they stood without food in front of them multiple times per day, they WERE upset if they could not eat their food “on time”. I suspect this was a legitimate physical discomfort for them as well as an anxiety issue. All of my horses experienced colic issues at one time or another while boarded, with the exception of the last barn I boarded at where they were out 24/7 & were fed free choice hay. None of them have had colic issues since being moved home a number of years ago. This tells me they have benefitted immensely from their current feeding schedule, which is as follows (if you are still reading & this hasn’t gotten too long!):
I feed a combination of alfalfa cubes/beet pulp/grain that is tailored to each horse and fed 3 times a day, given in a general 2 hour window.
-AM feeding is between 6:00-8:00am.
-Lunch is between 1:00-3:00pm.
-Dinner is between 9:00-11:00pm.
My horses are seldom excited for a meal… they sort of amble towards the barn when they realize I am in it. Sometimes I have to call them in & wait a few minutes for them to arrive (even in winter).
If we are experiencing extremely cold temperatures, I AM very mindful of spreading out their mash & grain meals in a way that keeps the window of time between their PM feeding & AM feeding on the shorter side.
I think, if you are boarding, your personal preference has to be modified by what you have available to your horses in regards to hay amounts and the turnout/grazing situation.