<?php
$content = <<<DATA
<body>
<div class="sm2-inline-duration timestamp">0:00</div>
<div class="sm2-inline-time timestamp">0:00</div>
<div class="sm2-inline-duration">0:00</div>
<div class="sm2-inline-duration">Do not touch this</div>
</body>
DATA;
$pattern = '/(<div\s+[^<]*?\bclass="[^<"]*\btimestamp\b[^<]*?>[^<]*)?(?<!:)\d{1,2}:\d{2}(?::\d{2})?(?!(?::\d{2})?\s*[ap]\.?m\.?)(?!.*?["\'])/';
$replacement = '[spp-timestamp time="$0"]';
return empty($m[1]) ?
'[spp-timestamp time="'. $m[0] . '"]' : $m[0]; }, $content);
echo $foundTimestamp;
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