if($_SESSION['1']){
$sql_comments_ad_1 = "INSERT INTO comments VALUES (0,'$assoc_0','$post_id','$comment_information','$total_time $time_actual')";
Deberías hacer un
isset($_SESSION['1']), también te falta cerrar el if, asi quedaría mejor:
if(isset($_SESSION['1'])){ $sql_comments_ad_1 = "INSERT INTO comments VALUES (0,'$assoc_0','$post_id','$comment_information','$total_time $time_actual')";
}
Tampoco declaras que usaras sesiones, aunque me imagino que la declara mas arriba.
if(isset($_SESSION['1'])){ $sql_comments_ad_1 = "INSERT INTO comments VALUES (0,'$assoc_0','$post_id','$comment_information','$total_time $time_actual')";
}