The answer will vary depending on what time it is...
Do you know what time it is on Saturday in Honolulu?
Well you are right, because it is not *always* Sunday in Japan!
Tokyo is Greenwich time + 9 hours (http://www.worldtimezone.com/time/wtzresult.php?CiID=4364&forma)
Honolulu is Greenwich time - 10 hours (http://www.worldtimezone.com/time/wtzresult.php?CiID=1221&forma)
That means they are 19 hours apart (Tokyo is 19 hours ahead of Honolulu).
If, for example, it's 2 AM on Saturday morning in Honolulu, it will be 9 PM on Saturday evening in Tokyo. Since the difference is only 19 hrs, and not 24, the book's statement is false.
Let me know if you have any questions. If not, thanks for pressing "Accept".