$call_start = strtotime(#תאריך ושעת שיחה#);
$call_end = strtotime(#תאריך ושעת סיום שיחה#);

$time_difference = $call_end – $call_start;
$hours = floor($time_difference / 3600);
$minutes = floor(($time_difference % 3600) / 60);

return str_pad($hours, 2, “0”, STR_PAD_LEFT) . “:” . str_pad($minutes, 2, “0”, STR_PAD_LEFT);