Unfortunately then, there is no way to get a bucketed Time Spent per Visitor.. this isn't provided out of the box, and we don't have the needed granularity in calculated metrics to achieve it... unfortunately, some metrics (like Time Spent per Visitor (seconds)) aren't available in segments, while others are....
The Total is showing you the proper de-duplicated UV count (as it should), the sum being more than the total will happen in many instances when using Unique Visitors or Visits metrics (since those metrics essentially "roll up" but also apply to individual rows of dimensions).
When you are looking at Time Buckets by Visit, then the same Visitor is going to appear in multiple buckets for each visit that they have (visit 1 the user was on the site for 6 mins, visit 2 the user was on the site for 2 mins, visit 3 the user was on the site for 17 mins, etc)
The display you are seeing isn't an issue, but understanding how to read and understand what is being presented is critical to such a report.
I usually add a description to any tables that have that to clearly explain to the people reading the report what it means and why it displays like that....
If you still really need a "Time per Visitor" your only real options are:
1. Log the new metric as an Idea (https://experienceleaguecommunities.adobe.com/t5/adobe-analytics-ideas/idb-p/adobe-analytics-ideas) and hope that someone at Adobe decides to proceed with it and make it a reality.. but this could be a long wait
2. You're going to have to export the raw data, bring it into something like a Data Lake, process it (i.e. making sure that excluded hits are excluded, and that you are properly stitching the visid_high and _low together to identify users) and then you will have to look at all the recorded time stamps in the time frame and calculate out how many Visitors fall in your own specified buckets....
Neither solution is ideal.
