Wrong time format

Drupal doesn't offer a time-only format, so a custom one is required to achieve the default layout. Knowing that bypassing Drupal's settings wasn't ideal, I made sure to make it easy to override the data format.

Add the code below to your template.php and change yourthemename to the name of your actual theme -- use the name of the directory it's in.

function yourthemename_activitystream_date($date) {
  $date = format_date($date, 'custom', 'g:ia');
  return $date;
}

Then change the date format to anything you'd like. You can use Drupal's short date format by doing something like this...

function yourthemename_activitystream_date($date) {
  $date = format_date($date, 'small');
  return $date;
}

Or you can use a time-only 24 hour clock like this...

function yourthemename_activitystream_date($date) {
  $date = format_date($date, 'custom', 'G:i');
  return $date;
}

See http://api.drupal.org/api/function/format_date for details about how to provide different date formats.