T.W.
I have the best result with eating REALLY GOOD and doing Billy Blanks Tae Bo. He has 30 minute work out videos that I do every other day. I also switch it up with the Total Gym. My goal is to do some sort of work out every day, even if it's for 15 minutes and working your core is VERY important.
I have the P90X system too and a lot of those videos are only 30 minutes.
Good luck!