Automatically refresh Cache

If in your magento system,magento cron jobs are working properly then you define a cronjob which fire on midnight and clear cache.

<crontab>
    <jobs>
        <clean_cache_midnight><!-- identifier -->
             <schedule>
                 <cron_expr>0 0 * * *</cron_expr> <!-- run cronjob on midnight -->
             </schedule>
            <run>
                <model>MyModule_Model_Group_Class_Name::functionName</model>
            </run>
        </clean_cache_midnight>
    </jobs>
</crontab>

And class is

<?php
class [ModuleNameSpace]_[ModuleName]_Model_Mycron
{
    public function functionName(){

     /**
     * Flush all magento cache
     */
     Mage::app()->cleanCache();
    }
}

Full module:

create config.xml at app/code/community/Amit/Cleancache/etc/

<?xml version="1.0" encoding="utf-8"?>
<config>
<modules>
    <Amit_Cleancache>
        <version>1.0.0</version>
    </Amit_Cleancache>
</modules>
    <global>
        <models>
            <cleancache>
                <class>Amit_Cleancache_Model</class>
            </cleancache>
        </models>
    </global>
    <crontab>
        <jobs>
            <clean_cache_midnight><!-- identifier -->
                 <schedule>
                     <cron_expr>0 0 * * *</cron_expr> <!-- running cronjob on midnight -->
                 </schedule>
                <run>
                    <model>cleancache/Fire::fireCacheonMidnight</model>
                </run>
            </clean_cache_midnight>
        </jobs>
    </crontab>
</config>

File2: create Fire.php at app/code/community/Amit/Cleancache/Model/

code:

<?php
class Amit_Cleancache_Model_Fire
{
    public function fireCacheonMidnight(){

     /**
     * Flush all magento cache
     */
     Mage::app()->cleanCache();
    }
}

File3: module config file Amit_Cleancache.xml at app/etc/modules/

<?xml version="1.0" encoding="utf-8"?>
<config>
    <modules>
        <Amit_Cleancache>
            <active>true</active>
            <codePool>community</codePool>
        </Amit_Cleancache>
    </modules>
</config>