Finally found it... It's like:

    if ( $from === $to ) {
        // Single day: Woo interprets this as "during that day in site timezone"
        $args['date_created'] = $from;
    } else {
        // Range: Woo interprets this as "between those days in site timezone"
        $args['date_created'] = $from . '...' . $to;
    }