This is exactly my routine with Grundy pony. She’s getting 2x a day, the other two get a couple snacks.
I fed once a day for the longest time and it was fine. The only time I ran into issues was when the horse needed meds AM and PM. Otherwise, for a small meal such as a ration balancer, I think it’s just fine.
Mine was on pasture, but it’s also not too hard to stock hay for the day depending on your set up.
They’re fine as long as their guts are kept moving. It’s a problem if they’re in a stall, dry lot etc with empty bellies all day As long as they have enough hay ur grass it’s fine