you can not know the exact leaving-china date. Even you know the date, it does not mean you will get it the parcel very soon. it might transit through many airports in different countries before arriving India.

Based on my experience, parcel will arrive India 2 to 5 weeks after shipment starting date. The arrival time is not accurate, however, you can know the exact arrival India date in http://track-chinapost.com/start_indiapost.php. Once the parcel enters India, the country column will show India instead of China and location will show India city name.