The skin electrical resistance graph of time vs kilo ohms illustrated on this site suggests that the most effective results are achieved at a time between 20 and 40 min. I would be interested in hearing any comments on this. The timing of meditation has been discussed here a couple of times. Apologies if I am going over old ground. Is there and effect from the relative speed of the mantra repetition on the cd?
To see the impact of meditation, "mind training" on personal happiness, have a look at the following video by a French Tibetan Monk:
http://www.ted.com/talks/view/id/191 .He reports the results of a very interesting scientific study that was carried out on the Tibetan "Olympians" of meditation - please excuse the irony. It is his phrase not mine.
Best wishes
Eoin