post_modifiedについて

###前提・実現したいこと
更新日時を設定したい。
###発生している問題・エラーメッセージ
更新日時が1970年1月1日となる

初投稿です、現在wordpressの更新履歴の改修を行っております。
post_dateをpost_modifiedに変換しようとしたところ
DBのpost_modified通りに表示されません。
更新日時が1970年1月1日となります
現状のソースをそのまま載せます。
wp_postsに接続

<div id="new">
	<div id="new_l"><img src="<?php bloginfo('template_directory');?>/img/new.png" alt="更新履歴"></div>
	<div id="new_r"><a href="/html/"><img src="<?php bloginfo('template_directory');?>/img/new_all.png"></a></div>
	<div class="clear"></div>
	<div class="shikiri"></div>
<div id="new_inside">
	
	
	
	
	
	
	
<?php
		$paged = (get_query_var('paged')) ? get_query_var('paged') : 1;//現在のページ数を設定




$blog_id = array('1','6','7','8','9','10','11','12','13','14','15');
$prefix = array('wp_','wp_6_','wp_7_','wp_8_','wp_9','wp_10_','wp_11_','wp_12_','wp_13_','wp_14_','wp_15_');
$name = array('a','b','c','d','e','f','g','h','i','j','k');







$wpdb_m = new wpdb('root','1415','wordpress','localhost');
$wpdb_m->set_prefix('wp_');
$test = $wpdb_m->get_results("
			SELECT post_title,post_date,guid
			FROM $wpdb_m->posts 
			WHERE post_type = 'main_post_a'
			AND post_status = 'publish'
			",ARRAY_A);
$test2 = $wpdb_m->get_results("
			SELECT post_title,post_date,guid
			FROM $wpdb_m->posts 
			WHERE post_type = 'main_post_b'
			AND post_status = 'publish'
			",ARRAY_A);
$test3 = $wpdb_m->get_results("
			SELECT post_title,post_date,guid
			FROM $wpdb_m->posts 
			WHERE post_type = 'main_post_c'
			AND post_status = 'publish'
			",ARRAY_A);	
$test4 = $wpdb_m->get_results("
			SELECT post_title,post_date,guid
			FROM $wpdb_m->posts 
			WHERE post_type = 'main_post_d'
			AND post_status = 'publish'
			",ARRAY_A);		
$test5 = $wpdb_m->get_results("
			SELECT post_title,post_date,guid
			FROM $wpdb_m->posts 
			WHERE post_type = 'main_post_e'
			AND post_status = 'publish'
			",ARRAY_A);		
$test6 = $wpdb_m->get_results("
			SELECT post_title,post_date,guid
			FROM $wpdb_m->posts 
			WHERE post_type = 'main_post_f'
			AND post_status = 'publish'
			",ARRAY_A);					
$test7 = $wpdb_m->get_results("
			SELECT post_title,post_date,guid
			FROM $wpdb_m->posts 
			WHERE post_type = 'sub_post_a'
			AND post_status = 'publish'
			",ARRAY_A);		
$test8 = $wpdb_m->get_results("
			SELECT post_title,post_date,guid
			FROM $wpdb_m->posts 
			WHERE post_type = 'sub_post_b'
			AND post_status = 'publish'
			",ARRAY_A);	
$test9 = $wpdb_m->get_results("
			SELECT post_title,post_date,guid
			FROM $wpdb_m->posts 
			WHERE post_type = 'sub_post_c'
			AND post_status = 'publish'
			",ARRAY_A);
$test10 = $wpdb_m->get_results("
			SELECT post_title,post_date,guid
			FROM $wpdb_m->posts 
			WHERE post_type = 'sub_post_d'
			AND post_status = 'publish'
			",ARRAY_A);	
$test11 = $wpdb_m->get_results("
			SELECT post_title,post_date,guid
			FROM $wpdb_m->posts 
			WHERE post_type = 'sub_post_e'
			AND post_status = 'publish'
			",ARRAY_A);	
$test12 = $wpdb_m->get_results("
			SELECT post_title,post_date,guid
			FROM $wpdb_m->posts 
			WHERE post_type = 'sub_post_f'
			AND post_status = 'publish'
			",ARRAY_A);	
$test13 = $wpdb_m->get_results("
			SELECT post_title,post_date,guid
			FROM $wpdb_m->posts 
			WHERE post_type = 'sub_post_g'
			AND post_status = 'publish'
			",ARRAY_A);	
$test14 = $wpdb_m->get_results("
			SELECT post_title,post_date,guid
			FROM $wpdb_m->posts 
			WHERE post_type = 'sub_post_h'
			AND post_status = 'publish'
			",ARRAY_A);					


for($x=0;$x<count($blog_id);$x++){
	$wpdb_m = new wpdb('root','1415','wordpress2','localhost');
	$wpdb_m->set_prefix($prefix[$x]);
	$test1 = $wpdb_m->get_results("
			SELECT post_title,post_date,guid
				FROM $wpdb_m->posts 
				WHERE post_type = 'contents_post'
				AND post_status = 'publish'
				",ARRAY_A);
    $test2 = $wpdb_m->get_results("
			SELECT post_title,post_date,guid
				FROM $wpdb_m->posts 
				WHERE post_type = 'sub_contents_post'
				AND post_status = 'publish'
				",ARRAY_A);

	for($i=0;$i<count($test1);$i++){
		$test1[$i][post_title] = $name[$x].'＞更新履歴＞'.$test1[$i][post_title];	
	}
	
	$test = array_merge($test,$test1);
}

$wpdb_m = new wpdb('root','1415','hands','localhost');
$wpdb_m->set_prefix('hs_');


$test1 = $wpdb_m->get_results("
			SELECT post_title,post_date,guid
			FROM $wpdb_m->posts 
			WHERE post_type = 'top_info'
			AND post_status = 'publish'
			",ARRAY_A);

for($i=0;$i<count($test1);$i++){
	$test1[$i][post_title] = 'c＞更新履歴＞'.$test1[$i][post_title];	
}


$test = array_merge($test,$test1,$test2,$test3,$test4,$test5,$test6,$test7,$test8,$test9,$test10,$test11,$test12,$test13,$test14);

usort($test, "array_sort");

for($i=0;$i<count($test);$i++){
	
?>
	<div class="news_box<?php if($box_backimg == 2){ echo'_gray'; $box_backimg = 0; } ?>">
		<div class="data_box"><?php echo date('Y年n月j日',strtotime($test[$i][post_date])) ?></div>
		<div class="text_box">

		<?php print('<li><a href="'.$test[$i][guid].'">'.$test[$i][post_title].'</a></li>');
		 ?>
		<?php
			$days=3;
			$today=date('U'); $entry=get_the_time('U');
			$diff1=date('U',($today - $entry))/86400;
			if ($days > $diff1) {
			echo '<span style="color:red;">NEW</span>';}
			?>
		</div>
	<div class="clear"></div>
	</div>
<?php
	
	
}


?>
		<?php wp_reset_postdata(); ?>

</div>
</div>