For ‘date’ data types:
Is it permissible to use a date-only format (e.g. yyyy-mm-dd), or is a full Datetime (yyyy-mm-ddThh:mm:ss) required?
Hi Kim,
It’s possible to use either the yyyy-mm-dd format or the combined date & time in UTC. 
ex. <meta class="swiftype" name="published_at" data-type="date" content="2017-06-20" />