Malaysian transiting in Beijing Capital airport for 21 hours

The first and the most important detail is that you are definitely eligible for 24 hour visa free transit and you do not need any kind of visa.

Now, to exit the airport, you will apply upon your landing, for a temporary entry permit at 24/144 hour visa free transit counter. This application is for free and here you will present your flight tickets along with a proof of pre-booked tour package, preferably in a printout form. This application is for free. Having in mind the length of your layover and your pre-booked tour that you plan to take, your chances to be granted a temporary entry permit are huge. I would say that the granting of permit is practically 99.9%.

Thank you for your advice.