The best way to prevent time constraints from stopping you exercising is to have a hand-full of intense exercise routines up your sleeve that take no longer than 20 minutes to complete.
When planning your workouts think about where you will be exercising and what types of exercise equipment will be available to you. When life is busy you may find it more convenient to train at home and use just bodyweight exercises or you may prefer to opt for interval training in a park or up a flight of stairs. The main thing is to plan workouts that suit your goals and to make it as intense as possible.
Keeping it simple normally works best for short workouts, basic exercise routines don’t have to mean easy!