How to go to Hong Kong International Airport in early morning from Tsim Sha Tsui Station area?

I have a returning flight to Jakarta on 7.55 HK Time on Saturday. And I'm staying in Kimberley Hotel, which is around Tsim Sha Tsui Station region. How do I get to airport on time, either by bus or by MTR? May I know when the A21 bus starts operating on every Saturday? And so does the MTR? In case of emergency, may I know how much does it cost if I take a taxi from Tsim Sha Tsui (near Kowloon Mosque) to HKIA?
Thank you very much for the help.

Regards,
Lin