$json = 'ваш json';
$array = json_decode($json);
$array = $array['channel_type']['1']['schedule'];
function comparator($one, $two)
{
$one_time = strtotime($one['start']);
$two_time = strtotime($two['start']);
if($one_time == $two_time)
{
return 0;
}
return ($one_time < $two_time) ? -1 : 1;
}
uasort($array, 'comparator');