Daily. I treat the seven bunnies as though they're four pairs (Boscov counts as two little bunnies when we're counting bellies) and then just divvy up what ever we've got into quarters. So one night they'll share a cauliflower, another night they'll share a bag of greens, the next night they'll get a few heads of broccoli between them. So if you work out how big an eighth of a medium sized cauliflower is, that's how much veg I give my bunnies each day. If I'm feeding carrots, then one carrot feeds three bunny bellies.
I feed both the veggies and the pellets in the evening so for the rest of the day they have nothing but hay. I don't like to feed veggies in the morning and the pellets in the evening (or vice versa) as it gives a fussy bunny the chance to avoid eating hay.