phpeveryday.com

<?php
$mm = 321;

// convert to hh:mm format
// result 05h 21m
echo sprintf("%02dh %02dm", floor($mm/60), $mm%60);
?>

<?php 
$hhmm = "05:21";

$arr = explode(":", $hhmm);
echo $arr[0] * 60 + $arr[1] . " minutes";
?>