Difference between durations - php

Question

I am creating a timesheet whereby it shows expected and actual hours.
The durations are saved like the below
23:15 - 23 hours and 15 mins
25:45 - 25 hours and 45 mins
I need to work out the difference in hours and mins between the two (extra hours worked)
I have tried the below
$acutal=='23:15';
$expected=='25:45';
$start_time = new DateTime("1970-01-01 $acutal:00");
$time = $start_date->diff(new DateTime("1970-01-01 $expected:00"));
This does work, however when the hours are over 24:00 it throws an error (obviously because it's reading it as time)
Uncaught exception 'Exception' with message 'DateTime::__construct():
Failed to parse time string (1970-01-01 25:45:00)
Is there another way to do this?

Answer 1

You could check if the number of hours are greater than 24, and if so, add a day, and remove 24 hours.
$actual='23:15';
$expected='25:45';
$day = 1;
list($hrs, $min) = explode(':', $expected);
if ($hrs > 24) { $day += 1; $hrs -= 24; }
$start_time = new DateTime("1970-01-01 $actual:00");
$time = $start_time->diff(new DateTime("1970-01-$day $hrs:$min:00"));
echo $time->format('%hh %Im');
Output:
2h 30m
Please also note that == is used to compare, not to assign.
You can also change the if ($hrs > 24) by while(), if there is 48 hours or more.
edit
As pointed out by #CollinD, if the time exceed the number of days of the month, it will fail. Here is another solution:
$actual='23:15';
$expected='25:45';
list($hrs, $min) = explode(':', $actual);
$total1 = $min + $hrs * 60;
list($hrs, $min) = explode(':', $expected);
$diff = $min + $hrs * 60 - $total1;
$start_time = new DateTime();
$expected_time = new DateTime();
$expected_time->modify("+ $diff minutes");
$time = $start_time->diff($expected_time);
echo $time->format('%hh %Im');

Answer 2

You can do it manually by keeping track of the number of minutes worked - this will be exact and will also allow you to show negative differences.
<?php
// get the difference in H:mm between two H:mm
function diff_time($actual, $expected) {
$diff_mins = mins($actual) - mins($expected);
return format_mins($diff_mins);
}
// convert a HH:mm to number of minutes
function mins($t) {
$parts = explode(':', $t);
return $parts[0] * 60 + $parts[1];
}
// convert number of minutes into HH:mm
function format_mins($m) {
$mins = $m % 60;
$hours = ($m - $mins) / 60;
// format HH:mm
return $hours . ':' . sprintf('%02d', abs($mins));
}
var_dump(diff_time('23:15', '25:45'));
var_dump(diff_time('25:15', '23:45'));
This outputs:
string(5) "-2:30"
string(4) "1:30"
.. first, 2:30 less than expected, for the second 1:30 more than expected.

Answer 3

You can try using datetime functions but it seems a lot more straightforward to me to treat the times as string, use split or explode to get hours and minutes, convert to integers, get the difference in minutes and convert it back to hours and minutes (integer divide by 60 and remainder).
$t1=explode(':',$expected);
$t2=explode(':',$actual);
$d=60*($t1[0]-$t2[0])+t1[1]-t2[1];
$result=str_pad(floor($d/60),2,'0',STR_PAD_LEFT).':'.str_pad($d%60,2,'0',STR_PAD_LEFT);