How hard you're working is more important than how long you're working. Your cardio work should be all about intensity. You often see people in the gym chatting and talking on mobile phones while on cardio equipment and you know that they aren't burning many calories.
It's better to do 30 minutes at a higher intensity than walk slowly for 45 minutes, you'll burn more calories too, and continue to burn them even after your workout. I'm not saying that you have to run for the entire time either. You can use a combination of fast walking and incline to achieve more intensity. I'd say that if you aren't burning at a minimum, 500-600 calories in those 45 minutes, you need to review the intensity of your routine.
Agreed.. Each to their own, but I do not get the phone thing. I come gym or run outside to get away from the damn phones ringing. I mean, I get you feel a need to prove you are so important you can't drop the phone even for a minute but they will wait..
You switch it up but I do some shorter cardio (40 mins) and I will be fucking pooling sweat, face red, hair drenched in agony like I feel the last 5 minutes are the worst of my lfe.. And afterwards , feel good! even if you only have 25 mins you can do that and bust some stress and maintain weight.