jsf-date-query-modify.php

<?php
add_filter( 'jet-smart-filters/query/final-query', function( $query ) {
		
	// replace this with values you need
	$meta_key = 'after';
	$date_format = 'Y-m-d\TH:i:s';
	
	if ( ! empty( $query['meta_query'] ) ) {
		foreach( $query['meta_query'] as $index => $row ) {
			if ( $meta_key === $row['key'] ) {
				$row['value'] = wp_date( $date_format, $row['value'][0] );
				$query['meta_query'][ $index ] = $row;
			}
		}	
	}
	
	return $query;
} );