if i buy a round trip ticket from tampa florida to guangzhou , can i apply for a 72 hours visa-free transit at guangzhou airport?

once i arrive,can i stay in guangzhou for 3 days , then take a bus or train to hong kong. after i finish all my business in hong kong, i will return to guangzhou city ( not airport ).can i apply 72 hours free transit again at immigration dept.?

if the answer is no . can i apply 72 hours free transit at guangzhou airport. then apply L visa at local chinese immigration dept. within next 3 days?
many thanks for your help !