Not very long. Someone who reads slower than average reads the entire thing in one year at just ten minutes a day.
See for yourself: www.howlongdoesittaketoreadthebible.com
There are 1189 chapters in the Bible, which means you read the Bible in a year at less than 3.3 chapters a day. Since a chapter is roughly a page in most Bibles, this means three pages a day and you’ve got it. Now, say you read eagerly, you know, the way you would if you thought the best-selling, most influential book in the history of the world was interesting and worthy of attention, not to mention God-breathed and inspired by the Holy Spirit. This would increase your reading speed. You would also need to not let yourself get bogged down, but to read comprehensively first in order to get the big picture. Afterall, could you imagine the Ephesians telling Paul it took them two weeks to read his six page letter because they got bogged down in word studies in the first chapter? It’s great to get bogged down in word studies, but only after you’ve made your way through the whole thing. By then, you are going to get a whole lot more out of the word studies anyway, having a bigger context to process them in. So if you speed up a bit your reading, say to 400 words per minute, which is faster than average but not by much, you can read whole thing twice in a year. Kick it up a real notch to 600wpm, and you’re at three times. It’s almost hard not to do it.