The format of block expiry timestamps returned from list=users and list=allusers has long been inconsistent. It was being returned in an internal format (e.g. "20190918201053"), rather than the ISO 8601 format used by the rest of the API (e.g. "2019-09-18T20:10:53Z").

The 'blockexpiry' property from these two modules will be changing to the standard ISO 8601 format with 1.34.0-wmf.24. See https://www.mediawiki.org/wiki/MediaWiki_1.34/Roadmap for a schedule of deployment to Wikimedia wikis.

This change also brings the block information returned by list=users and list=allusers fully in line with that already used for meta=userinfo and 'blocked' errors from various actions.