People will meditate for various lengths of time. At first, it may take a little longer to achieve the focus and clarity of mind needed to meditate. You may want to set aside an hour at first to make sure you are not rushing the process. Over time, with practice, some people find they only need five minutes to get something out of a meditation session.
I would recommend finding the length of time that works best for you and allow some flexibility if you find you need more or less time. It may be a few minutes or over an hour. Let your body and mind tell you.