Yes, it would be in each site's settings.php. There is no settings.php for "all". There is an issue about this that's been open for quite a while now. It comes and goes depending on the site and connection.
 
Nancy
Injustice anywhere is a threat to justice everywhere. -- Dr. Martin L. King, Jr.

From: Kenneth Jacker
  nw> In your settings.php file, put this line:
  nw> $conf['update_max_fetch_time'] = 60;

Which "settings.php"?  For each of my (multi)sites?

What about 'all'?

I changed it in 'default' and one of my sites, but
a theme (Zen) which appears updateable in the web
interface, but is not listed using Drush ("drush up").

Thanks again,

  -Kenneth

PS  Still puzzled why this change is needed ... has working
    fine for many months/years ...