I'm personally not really following the P90X or Insanity programs but I just recently added in the Insanity exercises to my workouts. I do Insanity 3 times a week 2 hrs after my dinner.
My workout setup is pretty much like this:
1)Pre lunch workout (strength/muscle building) 1hr
2)Post dinner workout (cardio/circuit) 35-50min depending on body fatigue
I think it's a pretty good workout and it makes you sweat while keeping ur heart rate up.