How can you add working hours to date time - sql-server

Question

I'm looking for a function where i can define working hours eg 9am - 5 pm and then add working hours to a datetime eg datetime 2021-08-05 16:30:00 add 3 working hours so the date time would be 2021-08-06 11:30:00.
I currently do this with working days see code below
This is to calculate SLA on a task eg task comes in at 2021-08-05 16:30:00 SLA is 3 working hours so it needs to be completed by 2021-08-06 11:30:00.
Any help would be appreciated
Thanks
declare
#ReturnDate datetime,
#StartDate datetime,
#CountDays int,
#Country varchar (255)
set #StartDate = '2021-08-05 16:30:00.000'
set #CountDays = 2
set #Country = 'England and Wales'
;with cteWorkingDates as
(
select DAT.Calendar_Date_Date,
ROW_NUMBER () over (
order by DAT.Calendar_Date_Date
) as RowNo
from dwBoyce.archway.Calendar_Date DAT with (nolock)
left join dwBoyce.archway.GovUK_BankHolidays BAH with (nolock) on DAT.Calendar_Date_Date = BAH.GovUK_BankHolidays_Date
and #Country = BAH.GovUK_BankHolidays_Country
where DAT.Calendar_Date_Date > #StartDate
and DAT.Calendar_Date_WorkingDay = 1
and BAH.GovUK_BankHolidays_Date is null
)
select cast(wd.Calendar_Date_Date as datetime) + DATEADD(day, 0 - DATEDIFF(day, 0, #StartDate), #StartDate)
from cteWorkingDates WD
where WD.RowNo = #CountDays

Answer 1

You might want to try the following:
Evaluate, how many minutes of working time are remaining starting from the time the ticket has been created. Then calculate the number of minutes the SLA request may take (in your case 3 * 60 = 180 minutes). When the remaining working time is less than the SLA time in minutes, the answer time will be Ticket time + 1 day + (SLA minutes - remaining working time in minutes).
Following an example:
DECLARE #WorkingHoursStart TIME = '09:00:00.000';
DECLARE #WorkingHoursEnd TIME = '17:00:00.000';
DECLARE #WorkingHoursCount INT = DATEDIFF(HOUR, #WorkingHoursStart, #WorkingHoursEnd);
DECLARE #SLAHours INT = 32;
DECLARE #TicketTimestamp DATETIME = '2022-11-01 12:30:00';
DECLARE #TicketWorkingHoursStart DATETIME = DATETIMEFROMPARTS(YEAR(#TicketTimestamp)
,MONTH(#TicketTimestamp)
,DAY(#TicketTimestamp)
,DATEPART(HOUR, #WorkingHoursStart)
,DATEPART(MINUTE, #WorkingHoursStart)
,0
,0);
DECLARE #TicketWorkingHoursEnd DATETIME = DATETIMEFROMPARTS(YEAR(#TicketTimestamp)
,MONTH(#TicketTimestamp)
,DAY(#TicketTimestamp)
,DATEPART(HOUR, #WorkingHoursEnd)
,DATEPART(MINUTE, #WorkingHoursEnd)
,0
,0);
DECLARE #TicketWorkingTimestamp DATETIME = CASE
WHEN #TicketTimestamp < #TicketWorkingHoursStart
THEN #TicketWorkingHoursStart
WHEN #TicketTimestamp > #TicketWorkingHoursEnd
THEN DATEADD(d, 1, #TicketWorkingHoursStart)
ELSE #TicketTimestamp
END;
DECLARE #TmpTimeStamp DATETIME = DATEADD(d, #SLAHours/#WorkingHoursCount, #TicketWorkingTimestamp);
DECLARE #TmpSLAHours INT = #SLAHours - ((#SLAHours/#WorkingHoursCount)*#WorkingHoursCount);
DECLARE #TmpSLAMinutes INT = #TmpSLAHours * 60;
DECLARE #AnswerTimestamp DATETIME = CASE
WHEN DATEDIFF(MINUTE, CAST(#TmpTimeStamp AS TIME), #WorkingHoursEnd) < #TmpSLAMinutes
THEN DATEADD(MINUTE
,#TmpSLAMinutes - DATEDIFF(MINUTE
,CAST(#TmpTimeStamp AS TIME)
,#WorkingHoursEnd)
,DATEADD(DAY
,CASE WHEN #TmpSLAHours/#WorkingHoursCount = 0 THEN 1 ELSE 0 END
,DATETIMEFROMPARTS(YEAR(#TmpTimeStamp)
,MONTH(#TmpTimeStamp)
,DAY(#TmpTimeStamp)
,DATEPART(HOUR, #WorkingHoursStart)
,DATEPART(MINUTE, #WorkingHoursStart)
,DATEPART(SECOND, #TmpTimeStamp)
,0)
)
)
ELSE DATEADD(MINUTE, #TmpSLAMinutes, #TmpTimeStamp)
END
DECLARE #WeekEndDaySkip INT = ((DATEPART(WEEKDAY, #TicketTimestamp)+DATEDIFF(d, #TicketTimestamp, #AnswerTimestamp))/7)*2
SELECT #TicketTimestamp AS TicketTime
, #AnswerTimestamp AS AnswerTimestamp
, DATEADD(d, #WeekEndDaySkip, #AnswerTimestamp) AS AnswerTimestampWOWeekend

Answer 2

Adding this deals with SLAs that span over weekends
declare
#date1 date = cast(#TicketTimestamp as date)
,#date2 date = cast(#TmpTimeStamp as date)
declare #Count int
Select #Count = count(*)
from archway.Calendar_Date d
where d.Calendar_Date_Date between #date1 and #date2
and Calendar_Date_DayName in ('Saturday','Sunday')
DECLARE #TmpTimeStamp1 DATETIME = case when #count = 2 then DATEADD(d,#count,#TmpTimeStamp)
else #TmpTimeStamp end