in dosearch.php

search for:
Code
  if (!isset($config['timesearch'])) {
	$config['timesearch'] = 60;
}


add underneath:
Code
if ($Forum == "All_Forums" &&
	$Words == "" &&
	$daterange == 1 &&
	$newertype == "d" &&
	$newerval == 1 &&
	$Limit == 25 &&
	$topic == 1 &&
	$fromsearch == 1) {
	    $config['timesearch'] = 0;
}



You can do the same based on other search criteria obviously.