Outside of a clinical setting, the significance of physical activity has been advocated for decades by many regional, national and international organizations. Influential people have been preaching these same messages for centuries.
Time is a fixed factor. You cannot create time nor take it away. You can only be more or less efficient with how you use it. Most of us have had periods where we've found it difficult, near impossible, to complete everything on our "to do" list within a given time frame. In times like these, physical activity is often the first thing to get the axe.
Short-term, sacrificing physical activity may pay off to get items A through Z on your list completed. Eventually though you'll have to "pay the piper". Edward Stanley's quote below sums this up nicely. Physical activity isn't the only thing that this applies to. For example, eating healthy typically involves more work and time than preparing any pre-made convenience food
Investing a set amount of time each day into physical fitness and healthy eating will be less time consuming than the time that's needed to manage the after effects of not taking care of your body (if not from additional health-related appointments then from a lower life expectancy). The big difference between these two scenarios is the quality of life you're likely to have.
Reframing your view on time, exercise and your future quality of life should put physical activity near the top of your "to-do" list. I've found writing Edward Stanley's quote on a piece of paper and sticking it on the fridge serves as a constant reminder to keep moving in times when there seems to be too much to do.