Can only purchase a product after X days

Hello,

I am afraid it is not possible to do by default but aMember is flexible enough and allow quite quickly
extends its functionality in any expect in upgrade proof way. In case of your task you can use the following code in
site.php to add such new feature:
http://www.amember.com/docs/Site.php_file

PHP:

//add new fields to product settings page
//aMember CP -> Products -> Manage Products -> (edit)
Am_Di::getInstance()->productTable->customFields()->add(
    new Am_CustomFieldText('c_days', 'Days',
        'require user to have active subscription to below product at least configured number of days in order to pucrhase current product'));
Am_Di::getInstance()->productTable->customFields()->add(
    new Am_CustomFieldSelect('c_pid', 'Required Product', '', null, array(
        'options' => array(''=>'') + Am_Di::getInstance()->productTable->getOptions()
    )));

//remove product from signup form if
//user does not meet configured requirements
Am_Di::getInstance()->hook->add(Am_Event::SIGNUP_FORM_GET_PRODUCTS, function(Am_Event $e) {
    $ret = $e->getReturn();
    $user = $e->getDi()->auth->getUser();
    foreach ($ret as $k => $product) {
        if (($d = $product->data()->get('c_days')) &&
            ($pid = $product->data()->get('c_pid'))) {

            if (!$user || $e->getDi()->db->selectCell("SELECT days FROM ?_access_cache WHERE fn=? AND id=? AND user_id=?", 'product_id', $pid, $user->pk()) < $d) {
               
                unset($ret[$k]);
            }
           
        }
    }
    $e->setReturn($ret);
});

You are welcome!