My app was approved on 22 January and so it is available since that date. In the same day I received this message from iAd Network
When you submit your app, ****, for approval, it will also be reviewed by iAd for use on the App Network to determine its appropriateness for receiving ads from iAd advertisers. Once your app is approved, you will be ready to start earning revenue for ads that run in your app.
But still today, no ads is showing. The "Ad Status" is Live Ads and "Impression" remains 0.
Apple announced on January 15, 2016 that it was shutting down the iAd service in June, and that no new apps would be accepted into the iAd program. Since that announcement predates your app's approval by a week, it's unlikely that you'll ever see any iAd ads show up. You should pull iAd out of your app and integrate some other ad provider instead.