If I'm in a rush I stretch for 20 secs in different variations for a total of 5 minutes. Keeping your body flexible and doing something is better than doing nothing. I like to focus on keeping a routine. I can increase the intensity whenever I find the time.
A walk is always a good rush exercise, plus you can add some arm circles while you do it or throw some punches, you can also get some high knees while doing it
Usually when I'm in a rush its usually because I need to get to work. In that case, i do not take a taxi to get to the bus stop. I instead take a walk. Grab a bottle of water, an apple and some mixed nuts. That way I'm getting my morning started right, I have the water for my first routine, apple and nuts as breakfast for my second and my third routine would be in progress on route to the bus stop. Simple, quick, easy and effective.
When I’m in a rush I think “What kind of exercise will I benefit more from today?” and take a few seconds to listen to my body before I decide which areas need to be exercised for a bit. If you trust what your body tells you (look for tension, discomfort or pain in any areas) you’ll find out which exercise will fit your day better and then just try to pick a few sets of might help you the most. If you’re feeling overall healthy then just opt for 10 or 15 minutes of cardio or yoga
If I'm in a serious rush, most of the time, I recommend waking up early in the first place. But if you are, try doing squats while brushing your teeth (for real, that saves time!) Or doing a short wallsit.