Using the following mdx, the result is the same if I run it with or without the where clause : It returns the total nbr of years in the hierarchy.
with member nbYears as [Time].[Year].[Year].count
select nbYears on 0
from [Sales]
where [Time].[2007]
You can use the Existing MDX function
WITH
member nbYears as (Existing [Time].[Year].[Year]).count
SELECT nbYears on 0
FROM [Sales]
WHERE [Time].[2007]