@elberet: Unfortunately I don’t speak Ruby and am not familiar with the Discourse internals and DB schema, and the SMF importer is quite different from the MyBB one (I guess the magic is in the MessageDependencyGraph class).
Could you point me towards how, for starters, to patch the MyBB script to convert the date in the quote line?
Also, how practical would it be to just go ahead with the migration, and later patch the quote line in the imported posts?