How early to start looking?

I'm currently a third year in university, going into my fourth. I am seriously looking into teaching English in Japan for a year or two. I just have a question that I haven't really been able to find an answer to: how early, or at least when in general, did you start searching if you were applying outside of Japan? How many months did the application process in general take if you applied to more than one company?

Also, I would like to return to Japan in December (as that is a month long break) in order to visit university friends, but as I don't graduate until May (thus meaning an August or September start), would that be too early to request for job interviews if they are needed (in Japan)? Would trying to use my smaller 1-week break in March/April or the summer be better?

I would highly recommend looking into the JET Programme. It has some of the highest pay and best support system available. Also, in the case you aren't accepted there is plenty of time to apply to other positions. The 2009/2010 application isn't available online yet but the deadline is around November and depends on which country you are applying through.

http://www.jetprogramme.org/