Extended event duration Millisecond or Microsecond?
It is a mix of Millisecond, Microsecond and some are unknown.  Easiest way to find I used below tsql code to determine which is what.

SELECT p.name package_name,
       o.name event_name,
       c.name event_field,
       DurationUnit= CASE
                         WHEN c.description LIKE '%milli%' 
                         THEN SUBSTRING(c.description, CHARINDEX('milli', c.description),12)
                         WHEN c.description LIKE '%micro%' 
                         THEN SUBSTRING(c.description, CHARINDEX('micro', c.description),12)
                         ELSE NULL
                     END,
       c.type_name field_type,
       c.column_type column_type
FROM sys.dm_xe_objects o
JOIN sys.dm_xe_packages p ON o.package_guid = p.guid
JOIN sys.dm_xe_object_columns c ON o.name = c.object_name
WHERE o.object_type = 'event'
AND c.name ='duration'


Here is the result set from a SQL 2016 SP1 server. I only posting part of it. Look at the DurationUnit column and you can see 3 different values.



For NULL ones I find the best option is to run (if possible with start and end time) and find what the unit is.

I ran the same query against vnext SQL Server and confirmed we will carry the same confusion to the future.