<?php

$html = "<div><h2>Hello world<h2><p>It's 7Am where I live<p><div>";
libxml_use_internal_errors(true);

$dom = new DOMDocument();
$dom->loadHTML('<root>' . $html . '</root>', LIBXML_HTML_NOIMPLIED | LIBXML_HTML_NODEFDTD);
$xpath = new DOMXPath($dom);

foreach( $xpath->query('//*[not(node())]') as $node ) {
    $node->parentNode->removeChild($node);
}
echo substr($dom->saveHTML(), 6, -8);