Get posts for last working week in WP_Query

Well, try the below code-

$base_array        = array(
    'posts_per_page'    => -1,
    'fields'            => 'ids',
    'post_type'         => 'cpt',
    'post_status'       => array('publish'),
    'date_query'        => array(
            'after'     => strtotime( 'previous week Monday' ),
            'before'    => strtotime( 'previous week Friday' )
    )
);

$base = get_posts($base_array);

I’ve not tested it. But I tested that below code returns the perfect date-

date('Y-m-d',strtotime('previous week Monday'));
date('Y-m-d',strtotime('previous week Friday'));

It returns-

2016-10-24 and 2016-10-28