Heard this tip yesterday and thought I would share.
To improve your posture and strengthen your abdominal core muscles and diaphragm, when you brush your teeth ....... stand on one leg! Right leg morning, left leg at night. The tiny, fine, imperceptable movements you make, to keep your balance whilst making the horizontal movements with your hand, are incredibly good for you.
So, you don't have to find any extra time at all, and you'll hardly notice the effort - though you might be a bit wobbly to begin with until your balance improves!
.......... and please do not sue me if you fall against the wash-basin!