It's stated under the iTunes Connect Developer Guide that:
After creating your app and it is in the state Prepare For Upload or Waiting For Upload, you have 180 days (6 months) from your creation date in iTunes Connect to deliver a binary to Apple. If you do not deliver a binary before the 180-day deadline, your app is deleted from iTunes Connect. As a result of this deletion, your app name can be used by another developer and you cannot reuse the app name, SKU or bundle ID.
All admin and technical iTunes Connect users on the developer's account will receive two warning emails as the expiration date approaches and one confirming the deletion of the App from iTunes Connect, once the 180 days deadline has been reached.
The first warning email will be sent when your App has been created for 150 days and no binary has been uploaded. The second and last warning will be sent when 173 days have passed.