Hi Sharon,
Keeping in mind that everyone is different and my body may not respond the same way yours does, but my body does not respond the same way to 30 min cardio as it does to 60 min cardio.
The best I can do with 30 min cardio x 6 days is maintain, possibly lose .5-1 lb., and that's only if it's "all Cathe" cardios, any other instructor means a maintenance week.
The only way for me to consistently shed pounds/inches weekly is with 4-6 days/week of 45-60min cardio, and then I can "usually" average 1.5-2lbs if my eating is good as well.
But this is me, and you may have great success with 30min cardios, so the best advice is to try it both ways and log your progress, then you'll know just what your body needs.
Donna