It is my opinion that it depends on the doe, and possibly how comfortable they are in their cage / barn / location.
I am sure a couple of my does feed at least twice a day, possibly even more, as the babies were always fat with full milk tummies no matter when I checked them.
I've also got does whose babies were never fat and seemed to just be surviving. I'm betting they only fed once a day.
I had a doe that I raised feed her babies during feeding time the other night.
It's been very cold and I've been spending minimal time in the barn, feeding, watering and doing chores. She, for whatever reason, picked that time to feed the babies.
I've also had does who were normally great Mama's suddenly nearly lose their babies. That's usually the first indication that I have some type of predator in the barn - a snake, rat, visiting possum, etc. The Mama's aren't comfortable showing where their babies are hidden, and thus don't visit to nurse them.