You can use 144 hours to explore the nice Cities of China like Beijing, but you need to follow some rules:
1.) This is a transit VISA, so is not possible to use a return flight to the same destination.
example: Germany > Beijing > Germany (not allowed)
but you can follow up like:
Germany > Beijing > HongKong and later go back to Germany (allowed)
The 144 hours starts after midgnight on arrival day. So you arrive on 21th Feb it starts counts from 22nd. You need leave the Aerea before midnight of the 26th.
2.) first register to Fingerprint Scanners in arrival Aerea
3.) go to special Counter for 144hour Visa Free (looking for 144h sign or ask any Service)
4.) Have ready Passport, Ticket with flight details to next destination (no RETURN), Hotel booking or confirmation of residence. If you not stay in Hotel you need also go through residence registration at the local police station. If you not following this rules you can be charged up to more than 2000 RMB.
5.) Fill out Arrical Card for temporary entry Foreigners (blue Form, not Yellow) May you already ask in Airplane to get it there and already fillout.
6.) Make sure you leave the country in time and to a thrid country (not origin Country). If you did not leave in time or try to get return to origin place you will be get a high penalty and 5years not access to 144h regulation. Maybe also not get any China Visum for normal proceedure.
7.) During communication with Chinese Immigration, Customs or Ground Airport Service Staff, keep in mind to talk slowly and clearly english. Keep on be friendly and smile, it makes everything fast friendliy and easy going.