For the OP as a first-time visitor, IMO it's better to allow more time to find your way through KL Sentral, the buses and the KLIA2 terminal as well as for bag drop. 3 am as I suggested earlier is perhaps a bit too early, but to allow 2 hours at the airport you should be on a bus by 3.40am.
You can take a train from Klia to Kuala Lumpur City Centre via KL Sentral in around 47 min. Alternatively, Sky Bus operates a bus from Kuala Lumpur International Airport to KL Sentral every 30 minutes. Tickets cost $3 and the journey takes 1h 15m. Three other operators also service this route. Train operators.Book a comfortable and hassle-free shared transfer service from KL Sentral to Kuala Lumpur International Airport 1 & 2. Take advantage of this service and enjoy a faster mode of transport to your destination! Sit back and relax aboard an air-conditioned and spacious bus during the trip. Meet your friendly AeroBus driver at the arrival hall of
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