Timing of divisional application before the Japan Patent Office (JPO)

Divisional application. When to file? The deadline.
So, you've got an office action from the JPO. And, you are going to cancel claims which you've not given up entirely. Then, file a divisional now. If your claims shall cover everything you want, or if it was filed on or after April 1, 2007, then, you can wait until the decision of rejection or the decision of patent is issued. But, never forget that once you get the decision of rejection, it will be the last chance to file a divisional application. And if your application was filed before April 1, 2007, then, it will not be possible to file a divisional application after decision of patent.

For more details, please see the following site.
http://www.jpaa.or.jp/english/patent/unique_jpo_practices.html#subcontents2
However, please note that the information provided in the site above is not up to date at this moment and you must read the text as follows.

(2) In an application filed before April 1, 2007, ..........
i. .............
ii. ..............
iii. After a Decision of Rejection is made, an applicant can file a divisional application within 30 days from the filing date at the same time with filing of a Notice of Appeal against the Decision of Rejection.

(3) In an application filed on or after April 1, 2007, .............
iv. After a Decision of Rejection is issued, an applicant can file a divisional application within 30 days three (3) months from the date when the applicant received the Decision of Rejection, (Art.44(1)(ii)); and
v. ....................