Does this apply as a layover for the 72 hour visa free transit in China ?!

If my route is a round trip from London to Shanghai and back to London, in this case a return ticket, but I'm staying less than 72 hours, does it apply for the 72 hour free transit policy or does my onwards destination have to be a completely different country alltogether ?!
And do I have to have a Chinese visa at all to be able to use the 72 hour rule or not ?!

Thank you.

Mario