I am familiar about the average time a US patent takes to get published but in Japan's case, I'm not sure.
Also, it would be great if you can tell me average publishing and grant time for other major countries.
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By "patent to get published" do you mean how long it takes to get patent granted and the publication of granted patent? Or do you mean how long it takes to the publication of patent application? The latter is normally 18 months. You may find some useful information about Japanese patent system here: http://www.epo.org/searching-for-patents/helpful-resources/asian/japan/faq.html