Create custom category template file.

category-daily.php

<?php

// Add newsletter signup box after 6th entry.
add_action( 'genesis_after_entry', 'theme_newsletter_widget_area' );
function theme_newsletter_widget_area() {

	global $wp_query;

	$counter = $wp_query->current_post;

	if ( 5 == $counter ) {

		genesis_widget_area( 'newsletter', array(
			'before' => '<div class="newsletter">',
			'after'  => '</div>',
		) );

	}

}

// Run Genesis loop.
genesis();