Question : How long do most people stay in Beijing when they fly in from Riyadh?
Answer : Of course you're not most people, but if you were, you'd stay roughly 15 days.
Question : Is price more important than specific travel days for you?
Answer : The cheapest day to fly in December is Sunday. Having flexibility in your travel plans means you can save, so be sure to plan ahead when possible.
Question : If punctuality is required for you to book a flight, which airline is your best bet?
Answer : China Southern Airlines will have you to PEK on schedule 100% of the time. Stick to China Southern Airlines and you won't spend more time in airports than you have to. Perfection is hard to come by, so hopefully it continues.