diferença entre minutos

<?php

$data = json_decode('{"start": "22:51", "hora": "24:35"}');
//$data = json_decode('{"start": "22:51", "hora": "24:35"}', true);

$start = strtotime($data->start);
$hora = strtotime($data->hora);
//$start = strtotime($data['start']);
//$hora = strtotime($data['hora']);

print round(abs($start - $hora)/60, 2) .  " minutos";

?>