For a schedule, such as http://futureofwebapps.com/london-2011/schedule/ (run the loop for each day). Needs to sort by time & then by track, ie. 2 sessions have an 11am start, 1 is 'Track 1' the other is 'Track 2'. 'Track 1' must be listed first.

Perch Custom Multisort

<?php
function array_push_assoc($array, $key, $value){
	$array[$key] = $value;
	return $array;
}

$opts = array(
       'template'=>'schedule.html',
       'page'=>'/page.php',
	'skip-template'=>true
);
$day1 = perch_content_custom('Day 1',$opts);
						
foreach ($day1 as $key => $session) {				
	if ($session['track1']) {
		$session = array_push_assoc($session, 'track', '1');
	} elseif ($session['track2']) {
		$session = array_push_assoc($session, 'track', '2');
	} else {
		$session = array_push_assoc($session, 'track', '0');
	}
	
	$track[$key] = $session['track'];
	$timestart[$key] = $session['timestart'];
    
	$day1[$key] = $session;
}

array_multisort($timestart, SORT_ASC, $track, SORT_ASC, $day1);

foreach ($day1 as $session) {
	// output sessions	
}
?>