I agree with Hazel, there's absolutely no need to do an hour. The lifeflow CD's last for that long for those who choose to meditate for that long. The downloaded lifeflow tracks are only 40 minutes long.
To get benefit from the entrainment tracks requires (so we are told) about 8 minutes for the brain to 'tune in' to the beats before the effects take hold. So, doing 10 minutes will give you a couple of minutes (thereabouts) of entrainment.
Most people who learn things like Transcendental Meditation, are started at about 5 or 10 minutes and over several weeks increase that time up to 20 minutes, with 20 minutes being the standard. After more experience this is often increased to 30 minutes. Some schools of meditation teaching suggest that more than 30 minutes in a single session offers no additional benefit, though some believe in extended periods of meditation.
As a beginner you sound like you're doing it just right, starting at a comfortable time and gradually building it up as you feel it is right. Aim to get to at least 20 minutes and you'll be well on your way.
Hugs
Giles