How to Divide Varchar(datetime) value in sql?

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SQL

How to divide This Varchar value in sql

Sql server 2008 running succeessfully.

Code in Sql:

DECLARE @TotalShiftHours varchar(50)
DECLARE @TotalWorkingHours varchar(50)
Declare @HalfDayCalculate varchar(50)
Declare @DivdeWorkingHours int

select @TotalShiftHours=convert(varchar,CAST(ShiftEnd AS DATETIME)-CAST(ShiftStart AS DATETIME), 8) FROM Accounts_DailyAttendance where UserID=1012 and DATENAME(MONTH,ProcessDate)='September' and DATEPART(YEAR,ProcessDate)=2014
----Total Working Hours Perday----
set @DivdeWorkingHours=2
select @TotalWorkingHours=convert(varchar,CAST(OutPunch_Time AS DATETIME)-CAST(Punch1_Time AS DATETIME), 8)  FROM Accounts_DailyAttendance where UserID=1012 and DATENAME(MONTH,ProcessDate)='September' and DATEPART(YEAR,ProcessDate)=2014
---HalfDay Calculate-----
set @HalfDayCalculate = convert(TIME(0), dateadd(second, datediff(second, 0, @TotalShiftHours) / @DivdeWorkingHours, 0))

select @HalfDayCalculate

But Sql server 2005 Half Day Calculate Not running, How to Half day Calculate in sql server 2005.

@TotalShiftHours='11:30:00'
set @DivdeWorkingHours=2
		
set @HalfDayCalculate = convert(TIME(0), dateadd(second, datediff(second, 0, @TotalShiftHours) / @DivdeWorkingHours, 0))

How to above query running sql server 2005 Get result is @HalfDayCalculate ='05:45:00'

Thanks