With exercise, I'm finding cycling to work and lifting weights are effective in terms of time. I spend half an hour of my day getting to work and back - probably about 10 minutes longer than it would take in a car. And with weight lifting, I never do any more than 3 sets of 10. The actual amount of time it takes is short.

This isn't exactly olympian conditioning, but I do notice a benefit and the time investment is low.