Here is a perfectly-matched pair for adding exercise to your daily schedule without taking time, while (probably) improving your mood and increasing your energy and concentration: Bicycling for low-intensity aerobic exercise, stairs for bursts of speed and strength. This would be a great addition to your life even if it weren’t the second most effective path to long-term health and lower risk of all causes of mortality.
The two greatest fitness inventions of all time (in my humble opinion) are the bicycle and the stairwell. Both fit into our city-dwelling lives, adding bursts of energy without taking time from our routines. Taking the stairs instead of the elevator is often quicker, and even for ten flights or more adds only 2 minutes or so, and starts your meeting or your workday with tension released, heart pumping, brain in high gear.
Similarly, a bicycle commute is almost always quicker than a bus or even a commuter train, when you take wait times into consideration. And bicycling may well be competitive with driving, if you include the time for parking and walking the last block or two to your destination.
Take a break from work every hour and run up a few flights of stairs. Stairs are conveniently available to most of us, and a minute of climbing is just the right scale for a high-intensity exercise break.
Celebrate the spring by bicycling to work one morning. Experiment with a new commuting routine.