Select any entity created today
You can use below code , PropertyCondition accepts range values using BETWEEN operator.. Since timestamp is stored as int in database node table created column with data and time together below code works to fetch records of a particular date..

&lt;?php
$day_start = strtotime(date('Y-m-d 00:00:00', $created_ts));
$day_end = strtotime(date('Y-m-d 23:59:59', $created_ts));
$query
    -&gt;propertyCondition('created', array($day_start, $day_end), 'BETWEEN');
?&gt;


Find more about propertyCondition in D.O