Blocked Process Report
This is only a partial answer as your requirements for viewing the reports in graph form are a bit vague for me, but that could also be because I tend not to aggregate blocking reports; instead I enable their collection on an as-needed basis.

This answer addresses the 5 second threshold.  As already pointed out by @Aaron Bertrand in the comments, blocking is a natural and expected behavior of SQL Server.  You can adjust the duration that blocking needs to occur before a query shows up in the Extended Event blocking report by adjusting the blocked process threshold (s) value via sp_configure.

The default value is 0, and while misleading isn't number of seconds, it means Off; all values greater than 0 refer to seconds.  The minimum number of seconds that blocking is required before queries will show up in the report is 1 second per my experience.  Also, take note that there are no guarantees when collecting blocked processes via the blocked process report.  As noted in the aforementioned article:


  The blocked process report is done on a best effort basis. There is no guarantee of any real-time or even close to real-time reporting.