USA>thailand>Beijing 72 hour visa

I'm a American passport holder and my wife is a Romanian passport holder. We are going from USA 20th> connect for 1 hour at Beijing 21th>Arrive at Thailand 22nd. Then returning to Beijing the 27th and leave on the 30th to USA. Do I qualify for the 72h? If upon my check-in to Beijing all I need to do is inform I need the 72 free transit or do I apply upon arrival at the immigration in Beijing?