Noob: format column in scaffold (i.e. - datetime)

This is my first RoR project so go easy. It’s a simple directory with
contacts. I have two datetime columns in my database (created_at and
updated_at). In the list view (changed very little from default
generated by scaffold) I want them to display as time_ago_in_words or
:long or :short (not sure yet). The default just takes up too much
space. In the show view this is fine and even preferred. I can’t figure
out how to change this before I render the list view. Presumably this
would be done in my directory controller, but I’m not sure and
everything I’ve tried doesn’t work. Thanks in advance.