we want to go with transmongolian to Ulan Batur after Bejing

Hi all,
is it possible to use the 144 hour exemption in the following way?
we would come with a return flight from Europe to Beijing
- stay in Beijing 5 days
- take the transiberian to Mongolia on day 6
- come back after 10 days to Beijing and fly back to Europe

would that work even if technically our return flight stay is actually 2 weeks considering we do not stay in China more than 6 days?