When I was getting renewable work permits (for working in a cram school), they were for a duration of one year or thereabouts, but here’s a 2014 post by someone who appeared to say he expected to get a three-year work permit:
Here’s a 2002 post by someone saying he got a two-year work permit:
Here’s a 2008 post by someone who said he had a three-year work permit:
A little incidental word of caution about the matter in the third quoted post (the 2008 post); I’m under the impression that joining the National Health Insurance program is mandatory for foreign workers (as to other people, I don’t know):