Are all FM3s for a year?

Question

Or can they be issued for less than a year?

Answer 1

A retirement FM3 is for a year.   A working FM3 is tied to a particular job and would have to be changed when job changes or is lost.

You can always leave the country  before the year ends if you choose

- I just remembered someone getting one for less than a year because their US passport had less than a year to go

Answer 2

Sometimes they are issued for less than a year when immigration is less than 100% convinced about your application. They will force a renewal after six months to make you prove that you still meet the income or other requirements.

Other (business) type visas are available for shorter terms.