fg_entryautomation_export_email_subject.php

<?php

add_filter( 'fg_entryautomation_export_email_subject', 'subject_date_range', 10, 4 );

function subject_date_range( $subject, $settings, $form, $file_name ) {

	// Get search criteria.
	$search_criteria = fg_entryautomation()->get_search_criteria( $settings, $form );

	// Add date range to subject.
	return sprintf( 'Form Summary for %s to %s', $search_criteria['start_date'], $search_criteria['end_date'] );

}