Converting seconds to date with Facet API
So it sounds like the issue is you need to convert a UNIX timestamp to a human-readable datetime?  PHP comes with the date() function which can handle this.

The first argument is the 'format' which you can find here: http://php.net/manual/en/function.date.php.  

The second argument is the UNIX timestamp--just simply pass in the timestamp variable (the # of seconds) as the second argument.