title: How to check the first date an app is installed?
body: <p>I have a paid app and want to offer it as free for a few days in the Store. But only for those who installed it during these special days I want to show ads.</p>
  
  <p>How can I check if a user installed the app in a specific time range?</p>
  
  <p><strong>I thought of these solutions:</strong></p>
  
  <ul>
  <li>I could have a sign in previous packages and check it in this
  package. if it was not available this was the first install.</li>
  <li>I could save the date after installation since the first time.</li>
  </ul>
  
  <p>But these won't work now.</p>
  
  <p>Thanks.</p>