Well are you asking when people feed
their horses or what
to and how much to feed your horse?
If it's the first question, the above posts give good advice, I personally do it twice a day. Whatever fits the needs of your horse and you. Also the horses get used to a schedule fairly quickly...
If it's the second question then we need to know a few things, like what breed is your horse (some are easier keepers then others)? His weight? Is he fat or skinny? Is he old or young?
What I have done, and it works very well, is to contact a knowledgeable feed man, and attack his brain.... Most people will tell you how many lb. A horse your size needs of whatever type of grain/hay... You'll have to go from there and watch the horse to see if he's getting fat, keeping good weight, or loosing weight...
In my opinion good grass has many nutritional values that we cannot find...Obviously my horses do better on it....So good healthy pasture would be #1 choice... And with most horses (that are easy keepers) that is all you'll need...Although when winter comes I like them to put on a bit more weight, but that's beside the point.