4
there is no setting to configure this, but with a small hack to the code you can make this happen:
in /modules/newbb/viewforum.php:
change:
$sortsince = !empty($_GET['sortsince']) ? intval($_GET['sortsince']) : 100;
to
$sortsince = !empty($_GET['sortsince']) ? intval($_GET['sortsince']) : [b]1000[/b];