Yes, that's a high standard, and it's not always possible. But if you count every type of physical exertion, from walking to stretching to crunches on your bedroom floor, over the course of a day you can usually reach this minimum level of exercise.
Most exercise specialists agree that if you can't do 30-45 minutes of cardio in one time period, it's okay to spread shorter bursts throughout the day. Take a 20-30 minute walk in the morning and another on your lunch break or after work -- whatever works best in your schedule. We bought a treadmill about a year ago and put it in our basement, where we also installed a television with cable hookup, so watching the Today Show before breakfast helps me to get through 30 minutes of cardio. It's been great in the cold, dark months when outdoor exercise is impractical.
But cardio exercise isn't the whole story. You also need to incorporate strength training and stretching. Pilates counts as strength training, and yoga gets the stretching in, making both of those practices quite beneficial.
A big change in my fitness routine has been that in October, I signed on to work with a trainer. She's helping me with strength, endurance, mobility and improving my posture. If you can't fit that into your life, then figure out some other way to do weight-bearing exercise at least a couple times a week.
I find that my health and happiness -- including managing stress -- depends on keeping up this exercise regimen. Exercise is vital. And remember, the more you exercise -- the more you can eat!