if you transfer from other places (I know the United States, Canada, Japan, France, Germany and the Netherlands, and of course it depends on your departure city in China), then any day will be fine.
If you have an American visa, it will be cheaper to transfer to Mexico via the United States.
Direct flight:
Aeromexico: Shanghai --> Tijuana, Mexico-> Mexico City
Every Thursday and Sunday at 1: 45 am, Shanghai Pudong Airport Terminal 2.