I don't know the official answer, but my GSD will not eat enough in 1 mealtime to meet the requirements for his weight, he would literally become an underfed dog simply because he has an annoying appetite. I can starve him for 2 days n he'll still eat the same amount of food at the meals I give him, so I feed him once in the morning and once in the evening. In the morning his appetite kinda sucks, I've figured out that if there's a threat of Lÿka stealing a few bites of his food that he's much more motivated to eat though, I hate to do it that way but he needs to learn that uneaten food disappears, n me taking it away doesn't seem to bother him as much as a lil girl walking in n sticking her nose in his bowl, n even then he gives it up, so I pull her away from the bowl n THEN he eats his food. For dinner I feed him 1.5x the amount I give for breakfast to total 2.5 cups of The Honest Kitchen per day, in actuality he eats about 2 or 2.25 cups and 12oz of ground beef, the minimum reccomended THK for his weight is 2.25 cups for an inactive dog... he is a moderately active dog and he eats the minimum. He would only eat 1.5 cups a day (and has done for several weeks in the past when I was following the "once a day pick it up in 10 minutes if he doesn't eat it" advice) if I fed once daily.
The pup I feed 3x a day, she eats the "Active Dog" amount for a 10-30lb dog, plus a little extra because she's a growing puppy. So she actually eats about 2.5-3 cups of THK a day, which is kinda sad because she's still skinny n eats more than a dog 3x her size. I also throw a lil ground beef in her food, maybe 2.5oz or so per meal. I gave her raw chicken wings n stuff too for a while but she started having stool problems so I went back to basics n only give her the occasional chicken wing or chicken quarter. I'll ease back into that and chicken gizzards again shortly, but being in a cast makes runny poop really suck for her, I see her "pumping" her cast leg to squeeze the last amount of runny poop out when her stools are loose LOL.
So I guess what I'm saying is it depends on the dog, I'm a big fan of 2 meals a day, but what matters is that the dog gets enough food. Also if the dog is a very active dog in the morning, or you do some kind of activity in the mornings then feeding once a day in the evenings might be better. I don't feed my dog in the morning unless it's more than 3 hours before we go training.