- explode: documentation ( source)
<?php
$day1hours = "10:15";
$day2hours = "10:15";
$day3hours = "04:00";
$day1 = explode(":", $day1hours);
$day2 = explode(":", $day2hours);
$day3 = explode(":", $day3hours);
$totalmins = 0;
$totalmins += $day1[0] * 60;
$totalmins += $day1[1];
$totalmins += $day2[0] * 60;
$totalmins += $day2[1];
$totalmins += $day3[0] * 60;
$totalmins += $day3[1];
$hours = $totalmins / 60;
$minutes = $totalmins % 60;
$totalhours = "$hours:$minutes";
echo $totalhours;