In 4.0, we will be allowing users to specify a startAtClusterTime option. Currently, the server expects the option to be a BSON document of the form:

{ ts: Timestamp }

This naming not intuitive, as a clusterTime object (as defined in server response $clusterTime.clusterTime) does not conform to this format.

We should either modify the startAtClusterTime field to expect a raw BSON timestamp, or choose a more intuitive name for the field.