The 3 x 30 mins per week is actually the least amount you should be doing and is really for people who are inactive and starting out. With the 30 mins not necessarily being in one go but accumulated over the day.
This link below is from the department of health and I think it has some excellent advice. Scroll down a bit to get to the adults activity part and then below that is also has advice for weightloss.
http://www.healthyactive.gov.au/interne ... l-activity
There are also some sites that set out not just the activity but the intensity of the activity but I can't remember which ones. It's not just a case of being active but you also want some of these activities to really get you huffing and puffing for an extended period. Great for weightloss and your heart will love it!
For me I found averaging 45 mins most days worked great in aiding my weightloss. I did cardio of around 45 mins 5-7 days a week (with the least being 5 days) with strength training twice a week at around 50 mins. Only on the days where I did cardio and strength training did I do more than an hr in the day.