有下面一个数组都是当天的时间

$a=array("9:00","9:30","10:00","10:30","11:00","11:30","12:00","12:30","13:00","13:30");

当前时间如果是10:00的时候：
排序后的数组是：
$a=array("10:00","10:30","9:30","9:00","11:00","11:30","12:00","12:30","13:00","13:30");

请问这个排序是如何实现的？