What are Reply Later Notifications or Reminders?

Once you have marked some emails as Reply Later, they appear as tasks with due time, sorted by urgency. When each such "task" reaches its designated time, you get a push notification as a reminder, to let you know that this was the right time for you to handle this mail, and make sure you get what you need, in the time that you asked for it. This is how you can really Get Things Done!