Question: I need to find how much time is between to time values (their difference) which are over 24:00:00.

For example: how can I calculate the difference between `42:00:00` and `37:30:00`?

Using `strtotime`, `strptotime`, etc is useless since they cannot go over 23:59:59 ....

Answer: 
```
$a_split = explode(":", "42:00:00");
$b_split = explode(":", "37:30:00");

$a_stamp = mktime($a_split[0], $a_split[1], $a_split[2]);
$b_stamp = mktime($b_split[0], $b_split[1], $b_split[2]);

if($a_stamp > $b_stamp)
{
 $diff = $a_stamp - $b_stamp;
}else{
 $diff = $b_stamp - $a_stamp;
}

echo "difference in time (seconds): " . $diff;

```

then use date() to convert seconds to HH:MM:SS if you want.
Date/Time variables and functions are not appropriate here as you're not storing time, but instead a time span of (I assume) hours, minutes, and seconds.

Likely your best solution is going to be to split each time span into their integer components, convert to a single unit (for instance, seconds), subtract them from each other, then re-build an output time span that fits with your application.