Last year I had to fill out the Customs 
Declaration form when I sent Global Priority and 
Global Express mail to Japan.  I haven't had to 
do so for several months now.  My understanding 
of the Global Express mail is that it is 
guaranteed to arrive in one day so long as it's 
within the United States.  After it arrives in 
Japan, it's up to their postal service to deliver 
the mail in a timely manner.  I would give it 
some more time.

- Jae