coe for spouse

if you just arrive in japan holding long term visa - descendant visa.

How many months before I can get my wife?

No real bottom wait limit.

But the longer you are employed. The more tax returns you have. The more time lived in Japan. The more savings and/or income. These all help.

If you have just arrived. That is too boxes that cannot be ticked. But doesn't mean it won't get approved.