Wait time percentage

How the Oracle DBA can find the Wait time percentage of the total DB time during the last hour.

DBA Oracle
Compatibility: Oracle 11g
Creator: Cyrille MODIANO – Montreal

SELECT
  metric_name,
  ROUND(AVG(value),1) "Average Wait time %"
FROM
   v$sysmetric_history
WHERE metric_name = 'Database Wait Time Ratio'
GROUP BY metric_name;