Most horses and ponies will pig out and eat all of it at once. I would not risk the possibility of colic. I'd have two different people stop by any way - and have a relative or friend stop by TOO, to make absolutely sure the other two were feeding the pony!!!
There was a high profile case in New England last year, where a woman went on vacation and the people she hired did not water and feed the horses.
It just so happened that Animal Control came out that day, and the horses had no water or food. All 6 horses were confiscated, and the woman was not allowed to get them back.
Honestly, if I were you, I would NEVER arrange such a thing. Too many things can go wrong. I'd board the pony at a good quality boarding stable, where someone is there much of the day in case the animal gets sick, and he will be guaranteed to get fed on a schedule.
I can't even count the number of situations I've heard of over the years where 'horse sitters' did not show up, nor all the problems that arose - sickness, injury where the animal stood there for days with no food water or medical care - not me. Not in a zillian years.
