DECLARE @start_date DATETIME
DECLARE @end_date DATETIME

SET @start_date = DATEADD(hour, 20, DATEDIFF(DAY, 2, GETDATE()))
SET @end_date = @start_date + 1

select @start_date, @end_date

This will also work:

DECLARE @start_date datetime
DECLARE @end_date datetime

SET @start_date = LEFT(CONVERT(nvarchar, DATEADD(DAY, -2, GETDATE()), 120), 11) + N'20:00:00'
SET @end_date = @start_date + 1

select @start_date, @end_date

Although cyberkiwi's answer is very clever! =)

I needed to pull a date from the database and append 3:00 Pm to it. I did it this way

select dateadd(hour, 15, datediff(day, 0, myDatabaseDate)) 
from dbo.myDatabaseTable
where myDatabaseId = 1

The result that it returned was 2017-10-01 15:00:00.000 . The date in the database is 2017-10-01 . The solution that I proposed was to keep my current date. I added 0 days to my existing date. I gave it 15:00 hours and it worked like a charm.

In case of just updating a particular part of the datetime you can use SMALLDATETIMEFROMPARTS like:

UPDATE MyTable 
SET MyDate = SMALLDATETIMEFROMPARTS(YEAR(MyDate), MONTH(MyDate), DAY(MyDate), <HoursValue>, <MinutesValue>)

In other cases it may be required to copy parts of datetime to other or update only certain parts of the datetime:

UPDATE MyTable 
SET MyDate = SMALLDATETIMEFROMPARTS(YEAR(MyDate), MONTH(MyDate), DAY(MyDate), DATEPART(hour, MyDate), DATEPART(minute, MyDate))

Refer SQL Server Date/Time related API references for more such functions

DECLARE @start_date DATETIME = DATEADD(HOUR, 20, DATEADD(MINUTE, 00, CONVERT(DATETIME, CONVERT(DATE, GETDATE())))) - 2
DECLARE @end_date DATETIME = DATEADD(HOUR, 20, DATEADD(MINUTE, 00, CONVERT(DATETIME, CONVERT(DATE, GETDATE())))) - 1

Notes:

• GETDATE() + X is the equivalent of DATEADD(DAY, X, GETDATE()) .
• Converting a DATEIME to a DATE and then back to a DATETIME again sets the time to midnight i.e. 00:00:00.000 .
• Seperate SET and DECLARE statements are unnecessary, but just in case it helps later, variables may be set as part of a SELECT statement too.

The solution is to convert time datatype into datetime and add

DECLARE @date DATETIME, @time time
SET @date='2023-10-01'

SET @time='15:00:00'
SET @date=@date+CAST(@time AS DATETIME)
SELECT @date AS DATETIME

The result is 2023-10-01 15:00:00.000

I had to do something similar, create a procedure to run from a certain time the previous day to a certain time on the current day.

This is what I did to set the start date to 16:30 on the previous day, basically subtract the parts you don't want to get them back to 0 then add the value that you want it to be.

-- Set Start Date to previous day and set start time to 16:30.00.000

SET @StartDate = GetDate()
SET @StartDate = DateAdd(dd,- 1, @StartDate) 
SET @StartDate = DateAdd(hh,- (DatePart(hh,@StartDate))+16, @StartDate) 
SET @StartDate = DateAdd(mi,- (DatePart(mi,@StartDate))+30, @StartDate) 
SET @StartDate = DateAdd(ss,- (DatePart(ss,@StartDate)), @StartDate) 
SET @StartDate = DateAdd(ms,- (DatePart(ms,@StartDate)), @StartDate)

Hope this helps someone.