PHP, Add gmdate to gmdate - php

Question

I have a code that looks like this:
$dagtidhelg = gmdate('H:i', $diffMorning) . "\n";
$kvallstidhelg = gmdate('H:i', $diffNight);
This code runs several times per page since its runt every time a row is loaded from mysql.
It can return a time value ie 08:15 and 09:30. This is the lenght of two work sessions.
That works great but now Im stuck, I want to display the total of every work session at the bottom. I have tried this:
$dagtidhelgtotal = $dagtidhelgtotal + $dagtidhelg;
$kvalltidhelgtotal = $kvalltidhelgtotal + $kvallstidhelg;
But that only adds the hours togheter, it wont even display the :
So Im guessing that Im doing this totaly wrong.
How can I add these times togheter? Maybe convert them to minutes, then add them all togheter?

Answer 1

Add duration together is simple .But you must keep in mind that duration and date are two things completely different. You can write 100:08 for duration but not for date. If your purpose is to keep a duration counter on(one or) every page(s) you need to build a system based on $_SESSION variable.
To add two duree you can proceed like this:
function addDuration($duration1,$duration2){
$result=array_map(function($x,$y){return sprintf("%'.02d", $x+$y);},explode(':',$duration1),explode(':',$duration2));
if($result[1]>60){
$result[0]=sprintf("%'.02d",$result[0]+(int)$result[1]/60);
$result[1]=sprintf("%'.02d",$result[1]%60);
}elseif($result[1]==60){
$result[1]="00";
$result[0]=sprintf("%'.02d",$result[0]+1);
}
return join(':',$result);
}
and the usage in your case could be:
$dagtidhelgtotal = addDuration($dagtidhelgtotal,$dagtidhelg);
if we suppose that
$dagtidhelgtotal ==='100:09' && $dagtidhelg === '08:08'
then after the addition
$dagtidhelgtotal will be equal to '108:17';