How Long To Meditate
For Beginners
Ideally you should try for at least 10 - 20 minutes a day, and you biggest problem will be controlling the "Monkey Mind"
from thoughts as they flood your brain.
This is easier to do than you realize and once you have mastered how to do this, your meditation will be much richer.
Semi-Advanced
If you have been doing meditation for a while - at least several months - you should be at the stage where 30 - 40 minutes is quite easy.
It is at this stage that you need to start focusing on "Intent" by using "Advanced Meditation"
which will give you a deeper realization of how to use your mind (and soul) to travel.
Advanced
Many people who have been meditating for a long time feel that they Know It All, but I would encourage you to kindly read this info about incorporating "intent" into your "Controlled Meditation"
routine.