I try to meditate at least 45 minutes a day, no matter what. I have found that, no matter what I am doing during the day, I can always find a little bit of time to formally pay attention to the quality of my thoughts.
You can do it anywhere. Standing up, sitting down, walking, laying down, etc. It's just focusing on your breath and the physical sensation of breathing, so, it's pretty simple.
So yeah, don't just do it when you're stressed! Do it everyday!