Original: It was not until a special bulletin was issued by the CPHC at 6:30 PM on September 10—less than 24 hours before landfall—that any warning was given to the public.
Simplified: It was not until a special bulletin was issued by the CPHC at 6:30 PM on September 10 - less than 24 hours before landfall - that any warning was given to the public.