Sometimes even 5 minutes is better than no exercise. For example, this morning I ran around the block, which is an 800, in approximately 6 minutes. Following up with a double-duty stretch completed my morning workout on a busy workday.
Start with the slant board stretch, one leg at a time. Lean against the wall with one hand, then take your opposite foot and do a quad stretch with the one leg while stretching the calf with the other. The following two videos from YouTube show each stretch separately; simply put them together when you feel ready.