A LearningObjectDates object looks like:

{
  // the ID of the learning object (not present for checkpoints)
  "id": 4,
  // the due date for the learning object. returns null if not present or
  // applicable. never applicable for ungraded discussions, pages, and files
  "due_at": "2012-07-01T23:59:00-06:00",
  // the lock date (learning object is locked after this date). returns null if
  // not present
  "lock_at": "2012-07-01T23:59:00-06:00",
  // the reply_to_topic sub_assignment due_date. returns null if not present
  "reply_to_topic_due_at": "2012-07-01T23:59:00-06:00",
  // the reply_to_entry sub_assignment due_date. returns null if not present
  "required_replies_due_at": "2012-07-01T23:59:00-06:00",
  // the unlock date (learning object is unlocked after this date). returns null
  // if not present
  "unlock_at": "2012-07-01T23:59:00-06:00",
  // whether the learning object is only visible to overrides
  "only_visible_to_overrides": false,
  // whether the learning object is graded (and thus has a due date)
  "graded": true,
  // [exclusive to blueprint child content only] list of lock types
  "blueprint_date_locks": ["due_dates", "availability_dates"],
  // whether the learning object is visible to everyone
  "visible_to_everyone": true,
  // paginated list of AssignmentOverride objects
  "overrides": null,
  // list of Checkpoint objects, only present if a learning object has
  // subAssignments
  "checkpoints": null,
  // the tag identifying the type of checkpoint (only present for checkpoints)
  "tag": "reply_to_topic"
}