UK to Beijing to Hong Kong, and back same way - is 72hour visa transit waiver applicable?

We have an upcoming trip where we'll be flying from the UK to Beijing, then (25 hours later) we fly Beijing to Hong Kong and stay for 4 days. We then fly back to Beijing, and (about 18 hours later) we fly to the UK. Am I correct in thinking we can use the 72 hour free transit visa in Beijing in both directions?

Thanks for your help :)