<?php

CONST TIME_DIFF = 10;
$time = '19:01';
printf("Current time: %s", $time);


$dTime = DateTime::createFromFormat('H:i', $time);
$minusTen = new DateInterval("PT" . TIME_DIFF . "M");
$dTime->sub($minusTen);


printf("\n10 minutes before: %s", $dTime->format('H:i'));