Dump this in template.php
function phptemplate_node_submitted($node) {
$time_unit = 86400; // number of seconds in 1 day => 24 hours * 60 minutes * 60 seconds
$threshold = 1;
if ($node->changed && (round(($node->changed - $node->created) / $time_unit) > $threshold)){ // difference between created and changed times > than threshold
return t('Last updated on @changed. Originally submitted by !username on @created.', array(
'@changed' => format_date($node->changed, 'medium'),
'!username' => theme('username', $node),
'@created' => format_date($node->created, 'small'),
));
}
else{
return t('Submitted by !username on @datetime',
array(
'!username' => theme('username', $node),
'@datetime' => format_date($node->created),
));
}
}
<?php print $submitted; ?>