I have edited your code to fit in your requirement. Please try following code and you will get what you are expecting. What you were trying to do was wrong, the query you are trying will not display correct result as you are trying to add Prev Last Login of particular user like you mentioned in your code above, actually you were suppose to use Prev Last Login of any users you have logged in to the site.
case 'lasttonow':
$db_prefix = elgg_get_config('dbprefix');
$joins = array("JOIN {$db_prefix}users_entity u on e.guid = u.guid");
$admin = elgg_get_logged_in_user_entity();
$times =$admin->prev_last_login;
$options['joins'] = $joins;
$options['wheres'] = "e.time_created >= {$times}";
$options['order_by'] = "e.time_created DESC";
$content = elgg_list_entities_from_metadata($options);
break;