another format

<li class="amp-wp-posted-on">
	<time datetime="<?php echo esc_attr( date( 'c', $this->get( 'post_publish_timestamp' ) ) ); ?>">
		<?php
		echo esc_html(
			sprintf(
				'Published at %s',
                date("Y-m-d H:i:s", $this->get( 'post_publish_timestamp' ))
			)
		);
		?>
	</time>
</li>