Here is a function based on what I found on the internet to sum time duration values in a table column:
SET @VarName = (SELECT cast(dateadd(S,sum(datediff(S,0,)),0) as time) from )
Note that the datediff function converts each time value to an integer number of seconds which are then summed. The dateadd function converts the total number of seconds in the column to smalldatetime. This is then casted to a time value.
Use this to add specific time duration values:
SET @VarName = CAST(DATEADD(S,( DATEDIFF(S,0,@TimeValue1)+DATEDIFF(S,0,@TimeValue2)+...+DATEDIFF(S,0,@TimeValueN) ),0) as time)