title: How to validate Joi date based on a relative date?
body: <p>I understand that you can do this to validate a date that it should be before the current datetime:</p>
  
  <pre class="lang-js prettyprint-override"><code>const schema = Joi.object().keys({
      date: Joi.date().less("now").iso().required()
  })
  </code></pre>
  
  <p>However, I would like to take it further and validate a field based on a relative date either to "now" or to another field.</p>
  
  <p>More spefically, I would like to validate a field to make sure that it is less than ("now" + 12 hours) or ("other field" + 12 hours).</p>
  
  <p>How can I do this?</p>