Convert Seconds to hours, minute, seconds (hh:mm:ss) in MDX

WITH MEMBER [Measures].[TimSpent (HH:MM:SS)] AS '[Measures].[Timespent]/ 86400', FORMAT_STRING = "hh:mm:ss"

SELECT [Assignment].[Element].[Element] ON ROWS, {[Measures].[Timespent], [Measures].[TimSpent (HH:MM:SS)]} ON COLUMNS

FROM [Activity]