SELECT TOP 1 DATEDIFF for each hour group
Assuming this is SQL Server, you can truncate datetime values to hours using this technique:

DATEADD(HOUR, DATEDIFF(HOUR, 0, @YourDateTimeValue), 0)


Using that as a grouping criterion, you can then use the FIRST_VALUE analytic function (assuming you are on SQL Server 2012 or later version) to get the first DATEDIFF(MINUTE, Created, Updated) per group:

SELECT DISTINCT
  x.CreatedHour,
  DiffMinutes = FIRST_VALUE(DATEDIFF(MINUTE, t.Created, t.Updated))
                OVER (PARTITION BY x.CreatedHour
                      ORDER BY t.Created ASC
                      ROWS UNBOUNDED PRECEDING)
FROM
  dbo.YourTable AS t
  CROSS APPLY
  (
    SELECT DATEADD(HOUR, DATEDIFF(HOUR, 0, t.Created), 0)
  ) AS x (CreatedHour)
;


Since the FIRST_VALUE function would return the result for every row of your table, it would return identical values for entries created in the same hour, thus giving you a lot of duplicates. It is to suppress those duplicates that the above query is using DISTINCT.