mex - lax - pek - sha - hkg

Im from Mexico and I have a us visa, my flight departures from mex to LAX to PEK, arrives to beijing airport at 6am aprox and then I would like to make a quick trip to the great wall and sleep in beijing, early next day take a flight or bullet train to Shanghai get to know the city all day, sleep in Shanghai and the next day catch a flight to Hong kong at night (8pm more or less) to sleep in hong kong so I dont extend my 72 hours, is that doable?