Использовать array_multisort:
<?php
$myarray=array(
0 => array
(
'dateTime' => '2011-10-18 00:0:00',
'chanl1' => '20.7',
'chanl2' => '45.4',
'chanl3' => '',
),
1 => array
(
'dateTime' => '2011-10-18 00:15:00',
'chanl1' => '20.7',
'chanl2' => '45.4',
'chanl3' => '',
),
2 => array
(
'dateTime' => '2011-10-18 00:14:00',
'chanl1' => '20.7',
'chanl2' => '33.8',
'chanl3' => '',
),
3 => array
(
'dateTime' => '2011-10-18 00:29:00',
'chanl1' => '20.6',
'chanl2' => '33.9',
'chanl3' => ''
));
foreach($myarray as $c=>$key) {
$dateTime[] = $key['dateTime'];
$chanl1[] = $key['chanl1'];
$chanl2[] = $key['chanl2'];
$chanl3[] = $key['chanl3'];
}
array_multisort($dateTime,SORT_ASC,SORT_STRING,$myarray);
print_r($myarray);