Calculate Time Difference in hh:mm - sql-server

Question

I have this query but I'm not sure what function to use so I can get time difference in this "hh:mm" format. Can anybody help ?
SELECT
EI.[FirstName]+' '+EI.[LastName] [EmployeeName], [Dpt].[FullName] [Department], [Desig].[FullName] [Designation],
FirstIN = CAST(MIN([AttendanceTimeIn]) AS TIME),
LastOUT = CAST(MAX([AttendanceTimeOut]) AS TIME),
HoursSpent = DATEDIFF(HOUR, CAST(MIN(AttendanceTimeIn) AS TIME), CAST(MAX(AttendanceTimeOut) AS TIME)),
CAST(COALESCE(AttendanceTimeIn, AttendanceTimeOut) AS DATE) [Date]
FROM [HRM].[tbl_Designation] [Desig], [HRM].[tbl_Department] [Dpt], [HRM].[tbl_EmployeeInfo] [EI]
FULL OUTER JOIN [HRM].[tbl_EmployeeAttendance] [Attendance] ON [Attendance].[EmpCode] = [EI].[ID]
WHERE
[Dpt].[ID] = [EI].[DeptCode] AND [Desig].[ID] = [EI].[DesignationCode]
AND
[EI].[RecordStatusCode] != '13'
AND
CAST((GETDATE()-1) AS DATE) = CAST(ISNULL([AttendanceTimeIn], [AttendanceTimeOut]) AS Date)
GROUP BY
EI.[FirstName]+' '+EI.[LastName], [Dpt].[FullName], [Desig].[FullName], CAST(COALESCE(AttendanceTimeIn, AttendanceTimeOut) AS DATE)

Answer 1

Maybe you can use something like this:
declare #d1 datetime = '2018-01-11 23:40:18.010'
declare #d2 datetime = '2018-01-12 11:59:18.010'
SELECT CONVERT(VARCHAR(2),DATEPART(HOUR,#d2 - #d1)) + ':' + CONVERT(VARCHAR(2),DATEPART(MINUTE,#d2 - #d1));

Answer 2

If to leave out your concept of using the time for the duration, you can use a query like below:
DECLARE #d1 DATETIME
DECLARE #d2 DATETIME
SELECT #d1 = GETDATE() - 1.465, #d2 = GETDATE()
SELECT
FirstIN = #d1,
LastOUT = #d2,
HoursSpent = CAST(DATEDIFF(HOUR, #d1, #d2) AS VARCHAR) + ':' + RIGHT('0' + CAST(DATEDIFF(MINUTE, #d1, #d2) % 60 AS VARCHAR), 2)

Answer 3

Let's expand step by step:
declare
#start datetime = getdate(),
#end datetime = dateadd(second, getdate(), 5000)
-- datediff(hour, #start, #end) -> hour difference
-- dateadd(hour, #start, datediff(hour, #start, #end)) -> start + integer hour difference to get less-than-an-hour diff
-- datediff(minute, dateadd(hour, #start, datediff(hour, #start, #end)), #end) -> minute difference from there
select
cast(datediff(hour, #start, #end) as varchar(2))
+ ':'
+ cast(datediff(minute, dateadd(hour, #start, datediff(hour, #start, #end)), #end) as varchar(2)) as [hh:mm]