Hong Kong Airport to LongGang, Shenzhen 518111 and return

First of all, Longgang is very large and it's impossible to estimate the travel time unclear about your final destination. Anyway, you may take a bus from HK airport to Shenzhen Bay Port or Huanggang Port, the duration is about 50 minutes; then cross the border and change to local transport, either subway train or city bus to your destination.