What conventional wisdom is that? The standard for warm up is 5 minutes isn't it? And a standard work out is 20-25 minutes as far as I'm aware. You can do a whole work out in 30 minutes.
My runs are 5 minutes warm up, I spend those 5 minutes walking to get from my house to a park, then 20-25 minutes running around the park (c25k plan) and then 5 minutes of walking back. You can fit that into almost any part of your day.
What about dressing up for the jog and afterwards showering and dressing up again? Also most people don't have a park in a 5 minute walking distance. I would say for most people they take 10-30 minutes to get to the training place, train at least 20 minutes and then 10-30 minutes back again and then 5-10 minutes of shower. Now that is quite a large part of the day.
My runs are 5 minutes warm up, I spend those 5 minutes walking to get from my house to a park, then 20-25 minutes running around the park (c25k plan) and then 5 minutes of walking back. You can fit that into almost any part of your day.