It's been 16 bytes, not 12, for ages. This was fixed in passing in HEAD
(commit
146604ec), but as a factual error it should have been back-patched.
Per gripe from Tatsuhito Kasahara.
</row>
<row>
<entry><type>interval [ <replaceable>fields</replaceable> ] [ (<replaceable>p</replaceable>) ]</type></entry>
- <entry>12 bytes</entry>
+ <entry>16 bytes</entry>
<entry>time interval</entry>
<entry>-178000000 years</entry>
<entry>178000000 years</entry>