How to set the CRON for every 4 hours?

I have created a custom cron group and below is the code.

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Cron:etc/cron_groups.xsd">
    <group id="MyCronJob">
        <schedule_generate_every>1</schedule_generate_every>
        <schedule_ahead_for>4</schedule_ahead_for>
        <schedule_lifetime>2</schedule_lifetime>
        <history_cleanup_every>10</history_cleanup_every>
        <history_success_lifetime>60</history_success_lifetime>
        <history_failure_lifetime>600</history_failure_lifetime>
        <use_separate_process>1</use_separate_process>
    </group>
</config>

In the cron group, I’m having 6 job instances and I want to generate the CRON for every 4 hours. so, I have updated the job instance as below

<job name="test_cron" instance="vendormoduleCrontest" method="execute">
            <schedule>0 */4 * * *</schedule>
</job>

Now my question is, in the CRON group, there is schedule_generate_every, so do I need to update the time in that portion as well and what is the difference which we are giving time in crontab and in crongroups.

Please guide and help.