The cheap answer is to set the timezone on the server to be in Japan's timezone. Of course, you would have an inverse error of sorts if you were to do some data entry - the datetime would be off.

Is the error coming from client-side validation? If so, you could adjust the validation to check the date as appropriate for the timezone.

Maybe a few more details would help me provide a better, non-kludge solution. We've used UTC in the past to adjust for timezones.

Take care,
Ric