Mine live outside and so are on the grass all day (which admittedly isn't that long during this time of the year). I put them out on the grass in their runs in the morning and fetch them in at dusk. They have water bottles in their runs, but apart from carrot tops, radish tops, etc., out of the garden if I'm picking for myself, they only have the grass (and the other edible weeds on the very weedy lawn) to eat.
At night, I give them 3 handfuls of pellets between 6 of them and usually half a carrier bag full of dandelions and other weeds between the 7 of them (my boy is on his own until he gets the op). The two rabbits get a large handful of said dandelions too. They have hay in a hay rack which I replenish as necessary (every few days). If I haven't been out foraging, then they get a bowl of carrot and other veg, or carrot/radish/turnip tops out of the garden. As they're on the grass all day, they only get fed once a day. They usually eat all of the pellets, so I just have to top that up. I change their water daily.
I enjoy taking my sister's dog for a walk and so take a carrier bag and forage for the guinea-pigs at the same time.