In the BFL book they recommend 20 minutes of cardio only but at a VERY high INTENSITY... Intensity is the key word here, and it does work... I still prefer to bring my cardio up to 30-60 minutes though ... But start with 20 minutes at high intensity you WILL definitely see a difference, then when you reach a plateau you can up the intensity more or make it a bit longer to kick start your body again, change is good when you are working out...
I personally feel that as long as you do some kind of workout throughout the day it does'nt matter when you do it as long as you DO IT! There are a a couple of good reasons to exercise in the morning though....1) It gets it out of the way...2) It revs up your metabolism for the rest of the day and 3) you will be in a better mood...
Hope this helps, don't be shy to ask more questions....