How long does it take the average person to read braille?

About as long as it takes the average person to read normal letters. Even less if you already know how to read normally, all you need to know is the letters and punctuation. It's not a difficult idea to grasp for most people. This isn't the same for everybody though. It does take a while to be able to reconize a mish-MASH of dots as letters, just as it takes a while to reconize a bunch of symbols (letters) as Words.