title: Android backup service - when and how often to backup?
body: <p>I want to backup my app's data using <a href="http://developer.android.com/google/backup/index.html">Android backup service</a>, but I'm concerned about network usage. I have about 500KB of data that needs to be uploaded for each backup operation. Not much, but if the backup is performed 10 times per day, it can easily reach 5MB. </p>
  
  <p>My question is, when and how often does Android decides to perform backup? The documentation only mentions "at an opportune time in the future" after I call <code>dataChanged()</code>. It doesn't explain what conditions constitute an "opportune time".</p>
  
  <blockquote>
    <p>You can request a backup operation at any time by calling
    <code>dataChanged()</code>. This method notifies the Backup Manager that you'd like
    to backup your data using your backup agent. The Backup Manager then
    calls your backup agent's <code>onBackup()</code> method at an opportune time in
    the future.</p>
  </blockquote>