Depends what your definition of 'Fit' is? Fitness is a relative term.
A 30 minute walk around a park somewhere is a great simple exercise though it won't keep you fit enough to run a marathon.
If you can get up early and go for a run/ go to the gym local it's a great idea to invograte your day
Alternately you could plan your day to be near a gym a couple of lunches a week.