DOCSP-13706 adding ttl deletion clarification (#1367)

* DOCSP-13706 adding delay clarification

* DOCSP-13706 adding -that- for consistency

* DOCSP-13706 adding ttl deletion clarification

* DOCSP-13706 adding -start- for context

* DOCSP-13706 updating tense for context

* DOCSP-13706 tech review comment implemented

Author: ltran-mdb

source/includes/fact-ttl-collection-background-timing.rst

@@ -1,12 +1,13 @@
 The TTL index does not guarantee that expired data will be deleted
-immediately upon expiration. There may be a delay between the time a
+immediately upon expiration. There may be a delay between the time that a
 document expires and the time that MongoDB removes the document from
 the database.
 
 The background task that removes expired documents runs *every 60
 seconds*. As a result, documents may remain in a collection during the
 period between the expiration of the document and the running of the
-background task.
+background task. MongoDB starts deleting documents 0 to 60 seconds after
+the index completes.
 
 Because the duration of the removal operation depends on the workload
 of your :binary:`~bin.mongod` instance, expired data may exist for some