Time spent per visitor distinct
I am trying to calculate time spent per visitor. Currently the time spent per visit - bucketed dimension is at a visit level only. If I use unique visitors as a metric, it totals to over what is shown in the column total - see screenshot:

When I total up what is the unique visitor column, it nets out to 32,258,363 not 25,307,565, as displayed in the UI.
Additionally, I cannot use the Total Seconds Spent metric in a Segment.
My goal is to understand Time Spent on Site per Visitor, uniquely. If a unique visitor spent 10 min one day on the site and 2 min another day on the site during the time same time period, I want their first visit to count once, and not be in two buckets in the Time Spent per Visit dimension.
Is there anyway to derive this?
