72 hours free transit with different airlines

Im in shanghai and i want to visit honk kong. i had a flight that comes back from hk on the 9th of august with a chinese company. the next morning i have a flight with another company to london. can i do the 72 hours free transit even if the companies are different to spend the night in shanghai? im asking this because i have already used a chinese visa with only one entry to stay in shanghai.