My personal experience with this is that two per day is a kind of threshold. It may be different for you - and the only way you'll find out is through experimentation - but when I tried three in one day, the effects seemed diluted and weak.
My inclination would be to listen to two each day, pairing ones that either build on each other or aim to achieve similar effects - Beliefs and New Behavior Generator, for instance. Ten Minute Supercharger sits well with anything - I use that one a lot, at a time when I might normally feel I needed a shot of caffeine.
Keep in mind also that both Belief and New Behavior Generator have two sessions each, and it's important to use both. Session A of Belief is for releasing old negative beliefs, while Session B installs new, positive ones. If you were going to do two sessions a day, it might be a good idea to do Session A and Session B in the same day.
These are all just suggestions. When it comes to this, the only real expert is you. Everybody has different goals, options, reactions and results with these things.
Hope this helps. Good luck!
