My own suggestion would be that a treasurer who is
an
appointed Board member would need to face the electorate not less than
six nor more than eighteen months after that appointment. The six
months should be enough time for him to put his mark on the job, and
show that he can communicate with the general membership.
Why would an appointed member ever have to seek election? The point of
appointed members is to get people with specific skills the board
requires, the point of election is to get people that can represent
the community. They are distinct goals, and you shouldn't try and mix
them. (Of course, if a member of the community has the required skills
and can fulfil both roles, that's great.)