The L-visa for international visitors is valid only 3 months after the date of issue, usually you are allowed to travel in China for 30 days in total. Therefore, you are suggested to apply for your China visa 1-2 months ahead of your travel date.

Some tourists apply for the visa after their arrival in Hong Kong if they don't have time to do it at home. You can request for an emergency service during the working days, and drop your passport one day before, and get it back the following day around noon time.