So this isn't my answer but I just found this while searching around online for a question like this as well. This guy set up a procedure to calculate hours, minutes and seconds. The link and the code:
--Creating Function
If OBJECT_ID('UFN_HourMinuteSecond') Is Not Null
Drop Function dbo.UFN_HourMinuteSecond
Go
Exec(
'Create Function dbo.UFN_HourMinuteSecond
(
@StartDateTime DateTime,
@EndDateTime DateTime
) Returns Varchar(10)
As
Begin
Declare @Seconds Int,
@Minute Int,
@Hour Int,
@Elapsed Varchar(10)
Select @Seconds = ABS(DateDiff(SECOND ,@StartDateTime,@EndDateTime))
If @Seconds >= 60
Begin
select @Minute = @Seconds/60
select @Seconds = @Seconds%60
If @Minute >= 60
begin
select @hour = @Minute/60
select @Minute = @Minute%60
end
Else
Goto Final
End
Final:
Select @Hour = Isnull(@Hour,0), @Minute = IsNull(@Minute,0), @Seconds = IsNull(@Seconds,0)
select @Elapsed = Cast(@Hour as Varchar) + '':'' + Cast(@Minute as Varchar) + '':'' + Cast(@Seconds as Varchar)
Return (@Elapsed)
End'
)