Adobe "bounce" metric shows 70K bounces. Time on page "bucketed" and "granular" metrics show 20K visits with time on page from 1 second to 30 minutes. If only 20K are actual visits then why does the original "visit" metric show 90K?
The time on page dimension needs atleast 2 hits in a visit to calculate Time spent and if there are more than 2 hits in a visit it is not considered as Bounce. Hence the against Time related dimension you will always see the proper visits.
Based on my understanding, if the visitor is landing on your site then the 1 Visit will be counted for that Visitor. But, after landing on your web site, if no other server call triggers then that Visit will be considered as Bounce. However, if a visitor lands on your site & performs any action link linking on a link then that Visit will not be considered as a bounce because now there are more than one server call which has fired in the visit. For more information on bounces, you can refer to the below link.
Any visit that includes a single call to Adobe Analytics call - and no more - is counted as a bounce. If 2 or more calls occur - page calls OR link tracking calls - the visit is not considered a bounce. Consider:
For every visitor who lands on the page, a page call is sent to Adobe Analytics. Each of these calls initiates a new visit. This represents the total number of visits: 90k
For every visitor who then leaves the site without performing any other action that would trigger a second (or third, etc) call to Adobe Analytics, a Bounce is calculated. This represents your 70k bounces.
For every visitor who has more than one call to Adobe Analytics, the visit is not considered a bounce. This represents the remaining 20k visits.