It depends how long it takes you to get into a good trance. You can actually practice meditation through out the day a few seconds here a few minutes there. You can meditate while you’re waiting in traffic, breaks at work, walking to your car, or even on an elevator.
I say be flexible with your meditation time anywhere from a few seconds to an hour. What you want to do is try to get into a trance state in a short time of beginning your meditation. You want to get good with trancing out quickly within a few seconds and maybe holding that meditative trance for as long as you feel is necessary for whatever it is that you want to accomplish.
Meditation = Hypnosis