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There are very informative threads on TWOV and doing transit at CAN in the China forum.
Most passports get 24 hour TWOV in China. Some can get 72 hours at CAN, although CAN calculates the 72 hours from the midnight after arrival IIRC, somewhat different from the 72 hour TWOV at PVG or PEK.
For either TWOV, you must genuinely transit to a third country and have a ticket receipt for the next flight. You can leave the airport, although you might be expected to show a confirmed hotel reservation.