MultidimensionalArraySubtraction

I have this array:
array (size=3)
  600 =>
    array (size=9)
      20090403 =>
        array (size=2)
          'atejo' => string '061359' (length=6)
          'isejo' => string '201030' (length=6)
      20090401 =>
        array (size=2)
          'atejo' => string '061607' (length=6)
          'isejo' => string '172359' (length=6)
      20090406 =>
        array (size=2)
          'atejo' => string '070951' (length=6)
          'isejo' => string '202657' (length=6)
      20090410 =>
        array (size=2)
          'atejo' => string '070956' (length=6)
          'isejo' => string '192603' (length=6)
      20090409 =>
        array (size=2)
          'atejo' => string '071208' (length=6)
          'isejo' => string '214419' (length=6)
      20090415 =>
        array (size=2)
          'atejo' => string '071257' (length=6)
          'isejo' => string '194741' (length=6)
      20090407 =>
        array (size=2)
          'atejo' => string '164836' (length=6)
          'isejo' => string '195309' (length=6)
      20090414 =>
        array (size=2)
          'atejo' => string '073737' (length=6)
          'isejo' => string '201052' (length=6)
      20090413 =>
        array (size=2)
          'atejo' => string '152621' (length=6)
          'isejo' => string '195248' (length=6)
  310 =>
    array (size=1)
      20090402 =>
        array (size=2)
          'isejo' => string '145639' (length=6)
          'atejo' => string '145813' (length=6)
  370 =>
    array (size=4)
      20090408 =>
        array (size=1)
          'atejo' => string '071738' (length=6)
      20090417 =>
        array (size=2)
          'atejo' => string '083641' (length=6)
          'isejo' => string '174714' (length=6)
      20090416 =>
        array (size=2)
          'atejo' => string '073629' (length=6)
          'isejo' => string '171001' (length=6)
      20090411 =>
        array (size=2)
          'atejo' => string '085419' (length=6)
          'isejo' => string '121022' (length=6)

I want to filter it via this filter and calculate differences between 'atėjo' and 'išėjo' times. And put them back into multidimensional array to keep the mapping of difference on the date for specified id.

foreach ($atvikimas as $k1 => $value1)
                                         {
                                                foreach ($value1 as $k2 => $value2) //$k2 personid
                                                {
                                                    foreach ($value2 as $k3 => $value3) //$k3 datos
                                                    {
                                                        //$atejimo_laikas = '';
                                                        //$isejimo_laikas = '';
                                                        if ($k3 == 'atėjo')
                                                            {
                                                                $atejimo_laikas = $value2[$k3];
                                                            }
                                                        else
                                                            {
                                                                $isejimo_laikas = $value2[$k3];
                                                            }
                                                        $abcd = $isejimo_laikas - $atejimo_laikas;
                                                        $isdirbtas_laikas[$k1][$k2] = $abcd;
                                                    }
                                                }


                                         }
                                         var_dump($atejimo_laikas);

So result should look like this, values should be difference between dates.
array (size=3)
  600 =>
    array (size=9)
      20090403 => string '061359' (length=6)
      20090401 => string '172359' (length=6)
      20090406 => string '202657' (length=6)
      20090410 => string '192603' (length=6)
      20090409 => string '071208' (length=6)
      20090415 => string '194741' (length=6)
      20090407 => string '195309' (length=6)
      20090414 => string '201052' (length=6)
      20090413 => string '195248' (length=6)
  310 =>
    array (size=1)
      20090402 => string '145813' (length=6)
  370 =>
    array (size=4)
      20090408 => string '071738' (length=6)
      20090417 => string '174714' (length=6)
      20090416 => string '171001' (length=6)
      20090411 => string '121022' (length=6)

I was given advice not to use 3rd foreach and to specify array's field, here what I get after it:

                                         foreach ($atvikimas as $k1 => $value1)
                                         {
                                                foreach ($value1 as $k2 => $value2) //$k2 personid
                                                {
                                                   //foreach ($value2 as $k3 => $value3) //$k3 datos
                                                   //{
                                                        //$atejimo_laikas = '';
                                                        //$isejimo_laikas = '';
                                                        if ($value2 == 'atejo')
                                                            {
                                                                $atejimo_laikas = $value2['atejo'];
                                                            }
                                                        else
                                                            {
                                                                $isejimo_laikas = $value2['isejo'];
                                                            }
                                                        $abcd = $isejimo_laikas - $atejimo_laikas;
                                                        //$isdirbtas_laikas[$k1][$k2] = $abcd;
                                                   // }
                                                }
                                         }
                                         var_dump($abcd);

Error report:

Undefined variable: atejimo_laikas

And it specifies this line: $abcd = $isejimo_laikas - $atejimo_laikas;

And I can't get var_dumps of $atejimo_laikas and $isejimo_laikas. Because, foreach can't find 'atejo' and 'isejo' index. So suggestion was illogical to the suggestion.

When I use third foreach, here is var_dumps of $k3 and $value3:

var_dump($atejimo_laikas);
var_dump($isejimo_laikas);
var_dump($k3);

string '085419' (length=6)
string '121022' (length=6)
string 'isejo' (length=5)

How should I make it continuesly subtracting $isejimo_laikas from $atejimo_laikas?
And store results in:
$isdirbtas_laikas[$k1][$k2] ($k1 is id and $k2 is str_replace "" "-" string).

foreach ($atvikimas as $k1 => $value1)
                                         {
                                                foreach ($value1 as $k2 => $value2) //$k2 personid
                                                {
                                                   //foreach ($value2 as $k3 => $value3) //$k3 datos
                                                   //{
                                                        //$atejimo_laikas = '';
                                                        //$isejimo_laikas = '';
                                                    $length = $value2['isejo'] - $value2['atejo'];
                                                     /* if ($value2['atejo'])
                                                            {
                                                                //$atejimo_laikas[] = $value3;
                                                                $length = $value2['išėjo'] - $value2['atėjo'];
                                                            }
                                                        else
                                                            {
                                                                $isejimo_laikas[] = $value3;
                                                            }*/
                                                       //var_dump($k3);
                                                        //$length = $value2['išėjo'] - $value2['atėjo'];
                                                        //$abcd = $isejimo_laikas - $atejimo_laikas;
                                                        //$isdirbtas_laikas[$k1][$k2] = $abcd;
                                                      //var_dump($length);


                                                }
                                         }