If I apply for 72h free transit, can i apply for tourist visa when Im in China before 72hrs expires?

RJ, I’m afraid you cannot do that.
Usually, only when the flight is delayed or one exceeds the permitted scope of stay due to for force majeure, one is allowed to apply for an entry permit at the local PSB. So you should apply for an entry permit in advance if you stay for more than 72 hours.