Katie Thear says you shouldn't feed wheat until later in the day, as it fills them up so they don't range as they should, and the wheat isn't a complete diet. She does recommend a scant handful of wheat each last thing at night as wheat is a hard grain and good for them to have in their crop overnight.
Until recently I've always followed her advice and given our totally free range free-loaders(*) a scattering of pellets in the morning, a small handful of wheat each at night.
Then I got myself in a tizz about the possibility of the ponies getting hold of the pellets, so decided to switch to mixed corn. Now they get a handful of that in the morning and a little at night if I see them and they seem perfectly healthy.
Mind, we're on a farm so there's always a bit of sheep or cattle cake about they can top up with.
(*) free-loaders because we feed them and the rotters hide their eggs from us if they possibly can!