tightened human time stamp validation regex
diff --git a/user_guide/changelog.html b/user_guide/changelog.html
index e0e2bef..207c594 100644
--- a/user_guide/changelog.html
+++ b/user_guide/changelog.html
@@ -67,6 +67,7 @@
<ul>
<li>Improved accuracy of calculations in <a href="helpers/number_helper.html">Number helper</a>.</li>
<li>Removed added newlines ("\n") from most form and html helper functions.</li>
+ <li>Tightened up validation in Date Helper human_to_unix(), and eliminated the POSIX regex.</li>
</ul>
</li>
<li>Other changes