By the time the cargo crosses the border the customs authorities ( to prepare ) already all the
necessary documents.

By the time the cargo crosses the border the customs authorities will have already
prepared

К сожалению, у нас пока нет статистики ответов на данный вопрос, но мы работаем над этим.

By the time the cargo crosses the border the customs authorities ( to prepare ) already all thenecessary documents.