Handling date to measure if "is working" or not

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PHP

I have two field related to an employee:

$enter and $leave ('08:00' and '18:00').

What I want to know, is that if that person is working "now" at current minute.

How can I handle this?

I did it this way:

$x = "18:00";
$y = "22:00";

//list($hour_enter,$minute_enter)= split('[:]', $x);
list($hour_leave,$minute_leave)= split('[:]', $y);

date_default_timezone_set('Europe/Lisbon');

$now= gmdate("H");
$z = $hour_leave-$now;

if($z > 0)
    echo "he's still working";
else
    echo "he already left";