"It is hard to imagine that, if the Sermon on the Mount really was a sermon, Jesus could have done it in less than an hour.I'm not a preacher, but I've done the Sermon on the Mount as an exercise with my small group. It takes around 30 to 40 minutes depending on how fast you go. My senior pastor performed a dramatic recitation of the entire book of Mark once. It took less than two hours. But Mark is the shortest Gospel.
Really, the bible is surprisingly compact and concise. I have an audio Bible. Well I had an audio bible. It's on extended loan at the moment. Start to finish you are looking at 65ish CDs. So the whole bible takes maybe 80 hours to read out loud. That's a lot if you're doing it in one shot, but I listened to the whole thing in about three months of commuting.