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:
The requierements for a patent are
(called non obviousness in the US)
Novelty is anchored in 35 USC 102, which reads
(a) NOVELTY; PRIOR ART.—A person shall be entitled to a patent unless—
(1) the claimed invention was patented, described in a printed publication, or in public use, on sale, or otherwise available ...
This is definitely an area where you are going to need to seek professional legal counsel. There are many issues here which will need careful navigation.
Depending on the invention there may be pending patents which could undermine your business case. Imagine investing large sums of money into a product only to discover that a patent was newly issued in ...