I am a bit confused as I also thought it was once a day. But this is one area in which I really do not know that much about. The HRS website though can have some conflicting info at times because they have great experts who write the articles, but may vary a bit. This article http://www.rabbit.org/care/newborn.html, it says the mother’s milk is rich enough to sustain babies for a 24 hour period. I wonder if the feeding twice a day is what may be causing the problem with her teats (in your other post).
In another article by Dana Krempels which was also in the HRS site http://www.bio.miami.edu/hare/surpriselitter.html, it says a mother may nurse once or twice, but it doesn’t say that it HAS to be twice.
And this article says feed NO more than twice a day, but that they are normally fed once a day. http://www.mybunny.org/info/newborn.htm and it seems that once is just fine if they are healthy. See paragraphs one two and three.
Again, this is just info that I have as common links for people who are dealing with new borns. I am VERY inexperienced when it comes to caring for babies, so I can only offer you other resources that I rely on.