I've combed many forum posts, websites, and the documentation page, but I am still unable to match exact figures for these two metrics.
Anyone managed to correctly derive the recipe to calculate bounces and time spent per visit/visitor?
Bounces would be the sum of visits for which 'visit_page_num' does not ever equal 2.
For time spent per visit/visitor, did you try following the steps below, but only subtracting the first hit from the last hit within the visit? Then summing to get a per visitor aggregate on site level.
How far off are your values from data feeds from what you see within the interface?