Cels Forum

    In Japan, only the larger post offices can handle the 
international postal money orders.  This is due to the issue 
of having to do currency exchange.  International Postal 
Money Orders can be redeemed at the Savings counter, which is 
only open Mon-Fri (closed on Sat, Sun, Holidays).  Even if 
the post office is open on weekends, the Savings counter 
is closed on Saturday and Sunday.   I believe they are open 
til about 4PM on weekdays, even if the rest of the post 
office is open til later.  
    To explain a bit more, at each post office, there is one 
part that deals with savings and other money issues (just 
like a bank), and the other part that deals with Mail.  The 
savings window has shorter hours.  
    Last time, I went to the large post office in Shinjuku 
to cash some US International Postal money orders.  The 
Savings department was on the 2nd floor.  The exchange rate 
was quite good, and there was no fee.  It was fairly quick 
and easy to do.

 -Leaf