My schedule is as follows:
Dried food topped up in the morning if needed (mine don't eat a lot of pellets so I don't always top up) and then left down all day - so readily available. They have more in the winter than in the summer.
Hay - mixture of different hays topped up 3 times a day - so always available
Veggies - fed twice a day, once at breakfast time, 2nd at tea time. About an hour after I put it down I go back and take the veggie bowls out - there is rarely anything left but if there is I do remove it.
I don't think you need to be too strict in terms of times but piggys do learn routine really well so I try and keep veggie times as regular as I can! Hay and water should always be available. I would be careful about leaving veggies down all the time as, especially in the summer, they can go a bit yuck after a while - which is why I always go back and take out the bowls and left overs.
Not saying this is the 'right' way but it works for me and my piggys!