Output meta into arrays

Add 'fields' => 'ids' to skip setting up the post and just create the array you want in the foreach.

$week_args = array(
    'posts_per_page' => - 1,
    'post_type'      => 'post',
    'post_status'    => array( 'publish' ),
    'fields'         => 'ids',
    'date_query'     => array(
        'before' => 'next Saturday',
        'after'  => 'last Monday',
    ),
);

$week_array = get_posts( $week_args );
$week_count = count( $week_array );

printf( '<h1>%s posts this week</h1>', $week_count );

$dates = array();
foreach ( $week_array as $post_id ) {

    $login  = get_post_meta( $post_id, 'meta_login', true );
    $logout = get_post_meta( $post_id, 'meta_logout', true );

    $dates[ $post_id ] = array(
        "meta_login"  => $login ? $login : 0,
        "meta_logout" => $logout ? $logout : 0,
        "dif"         => abs(strtotime($logout) - strtotime($login)),
    );
}

echo "<pre>";
print_r( $dates );