You will have to take a lengthy bus ride over to the Low Cost Carrier Terminal. When all is said and done, immigration, customs in the main terminal, 0-20 minutes wait for the bus, ~20 minute bus ride, check in at least 45 minutes before departure as per AirAsia requirements, figure 2 hours minimum if you are the adventurous type without checked bags, 3 hours or more minimum if you are the conservative type.