Hi schneid,
Your assumption is correct.
The Total Reviewer Time metric can explicitly be calculated by querying the activity table of Collaborator.
In the table, each row represents a slice of time where the user was active. There can be many slices for a given user in a single review. Each slice includes duration (in seconds) and "start time" that is encoded both as database date/time (activity_startdate) and a number of seconds since 1970-01-01 00:00:00 GMT (activity_startsecs). The activity_code column of the table tells whether the user was acting in the capacity of an author (A), reviewer (R), or was doing rework (F) as opposed to actually reviewing. Also, there is a code for when someone views the review but is not a participant (P).
Thus, the metric is a sum of all the durations of each reviewer activity (R) associated with a given review.
