Flight in to Beijing Train out next day to Mongolia

Our flight arrives Beijing at 07:25 am on a Tuesday and we depart by train on the very next day/Wednesday at 11:22 am. Can the 24 hour transit rule still work for us? The only reason we come to China this trip is to catch the train to Mongolia from Beijing, then we continue to Moscow on the Trans Siberian Railway. We fly out from St. Petersburg back to Australia without returning to PRC.