Dogs are more or less scavengers. They'll eat what is available, when they find it, due to not knowing when the next meal may be.
My last dog, and my current dog, got used to having food constantly around, as we'll put food in their bowl in the morning and at night. Not sure how we started with my first dog, but this one, we started by getting her to eat all of the meal twice a day, so we could kind of regulate her need to crap, which is good as a puppy. But she's grown in to just eating here and there, and rarely will eat all of what is in her bowl in one sitting. She knows its there, and doesn't need to devour it.
She was born on a farm, and her mom was definitely the scavenger. Got some food when she could, and even regurgitated some for the puppies.
Oh, and there are food dispensers that let the dog push a button to get food in the bowl. It's not actually hard to train a dog to make use of these, and if it gets comfortable with it, it'll just eat when it feels the need and, in effect, it feeds itself. Just need to pour a bunch of food from the bag into the container.
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