If I am travelling from either Lo Wu station or Lok Ma Chau station of New Territories(HK),

From Lo Wu, it takes about 84 minutes. From Lok Ma Chau, it takes about 89 minutes.

To reach airport, you need to the MTR as well as the Airport Express and the fee is charged seperately. For the MTR section, the fee is around 43.5HK$ and for the airport express, it is around 60HK$ (assuming transfering at Tsing Yi Station).