My outfit does 35 minute turnrounds on the 73, which is achievable. Probably 30 minutes can be done if all goes according to plan. But 20 minutes? Do the flight crew actually get out of their seats in that time? I can accept the "it flew in, it will fly out again" philosophy on a short turnaround, but I am still enough of a self-preservationist to want a check against tyre damage, birdstrikes etc, which can occur without the crew's knowledge.