Overriding the method post_meta_when() in your theme (file qa-theme.php) with custom time formatting should do what you want. I'm using something similar to this in my own theme:
function post_meta_when($post, $class) {
if (array_key_exists('otime', $post['raw']) and $post['raw']['_type'] !== 'Q') {
$this->_format_timestamp($post['raw']['otime'], $class);
} else {
$this->_format_timestamp($post['raw']['created'], $class);
}
}
private function _format_timestamp($timestamp, $class) {
$interval = qa_opt('db_time') - $timestamp;
$fulldatedays = qa_opt('show_full_date_days');
if ($interval < 0 || (isset($fulldatedays) && $interval > 86400 * $fulldatedays)) {
$gmdate = gmdate('Y-m-d H:i:s e', $timestamp);
$post_when = array(
'data' => '<time itemprop="dateCreated" datetime="' . $gmdate . '" title="' . $gmdate . '">' . $gmdate . '</time>',
);
} else {
// ago-style date
$post_when = qa_lang_html_sub_split('main/x_ago', qa_html(qa_time_to_string($interval)));
}
$this->output_split($post_when, $class . '-when');
}