70.5 hours stay in Shanghai

Good morning,

I am travelling from San Francisco to Shanghai for 70.5 hours (difference between time of arrival flight and departing flight) and then on to Singapore, part of a round the world trip ticket. Is it possible for me to benefit from the 72 hours visa free policy?
How should I proceed upon arrival in Shanghai? Shall I call the airline first to warn them about this?

Many thanks.

Best regards,

Paul