I fly a fair amount of Air China. On their domestic flights, yes, they are often late and sometimes cancelled so this is a real risk. Also, finding an English speaking person after check-in isn’t common. Transiting through Beijing takes a minimum of 2 hours but I would never plan less than 4 hours. Waiting in line is a way of life in China and there will be people bushing and cutting, it would be amusing if it wasn’t so frustrating. Lastly Shenzhen Airlines is part of Air China and it’s customer service is not as good as Air China, it’s the budget partner, the staff is nice but the schedule is only a rough estimate. My bottom line is I rarely make Internationnal connections through China and never without a minimum of a 4 hour layover and don’t include a domestic leg within China, it’s just too risky.