<?php
$timezone = "America/Detroit";
$today = new DateTime("Now", new DateTimeZone($timezone));
$myVar = "2015-04-19";
$dateCheck = new DateTime($myVar, new DateTimeZone($timezone));
/* Get the difference between today and the variable you are checking */
$diff = $today->diff($dateCheck);
// echo '<pre>' . print_r($days, 1) . '</pre>'; // This will give you the options you can do with the object:
if ( $diff->days >= 7 && $diff->days <= 30 ) {
echo "Display " . $dateCheck->format("F j, Y") . " because it's between 7 days and 30 days ago";
}