It was noticed recently that these blockinfo properties return the internal value from the database for the blockexpiry field, rather than formatting them as does list=blocks. This means the formatting is more difficult to parse, and that it may differ between installations of MediaWiki depending on the database backend in use, and it doesn't match the formatting of other timestamps returned by the API.

If anyone objects to this field being changed to be formatted in the same manner as the expiry field returned by list=blocks, speak up on the mediawik-api list.[1]

Thanks.

[1]: https://lists.wikimedia.org/mailman/listinfo/mediawiki-api