Make a table...

CREATE TABLE [Daylightsavings](

[PK_dst_key] [int] IDENTITY(1,1) NOT NULL,

[dst_year] [int] NULL,

[dst_begin] [date] NULL,

[dst_end] [date] NULL,

[dst_diff] [int] NULL,

PRIMARY KEY CLUSTERED

(

[PK_dst_key] ASC

)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]

) ON [PRIMARY]

INSERT the daylight savings start and stop times plus the offset to use.

insert into Daylightsavings

(dst_year,dst_begin,dst_end,dst_diff)

values

(1980,'1980-04-27','1980-10-26',1),

(1981,'1981-04-26','1981-10-25',1),

(1982,'1982-04-25','1982-10-31',1),

(1983,'1983-04-24','1983-10-30',1),

(1984,'1984-04-29','1984-10-28',1),

(1985,'1985-04-28','1985-10-27',1),

(1986,'1986-04-27','1986-10-26',1),

(1987,'1987-04-05','1987-10-25',1),

(1988,'1988-04-03','1988-10-30',1),

(1989,'1989-04-02','1989-10-29',1),

(1990,'1990-04-01','1990-10-28',1),

(1991,'1991-04-07','1991-10-27',1),

(1992,'1992-04-05','1992-10-25',1),

(1993,'1993-04-04','1993-10-31',1),

(1994,'1994-04-03','1994-10-30',1),

(1995,'1995-04-02','1995-10-29',1),

(1996,'1996-04-07','1996-10-27',1),

(1997,'1997-04-06','1997-10-26',1),

(1998,'1998-04-05','1998-10-25',1),

(1999,'1999-04-04','1999-10-31',1),

(2000,'2000-04-02','2000-10-29',1),

(2001,'2001-04-01','2001-10-28',1),

(2002,'2002-04-07','2002-10-27',1),

(2003,'2003-04-06','2003-10-26',1),

(2004,'2004-04-04','2004-10-31',1),

(2005,'2005-04-03','2005-10-30',1),

(2006,'2006-04-02','2006-10-29',1),

(2007,'2007-03-11','2007-11-04',1),

(2008,'2008-03-09','2008-11-02',1),

(2009,'2009-03-08','2009-11-01',1),

(2010,'2010-03-14','2010-11-07',1),

(2011,'2011-03-13','2011-11-06',1),

(2012,'2012-03-11','2012-11-04',1),

(2013,'2013-03-10','2013-11-03',1),

(2014,'2014-03-09','2014-11-02',1),

(2015,'2015-03-08','2015-11-01',1),

(2016,'2016-03-13','2016-11-06',1),

(2017,'2017-03-12','2017-11-05',1),

(2018,'2018-03-11','2018-11-04',1),

(2019,'2019-03-10','2019-11-03',1),

(2020,'2020-03-08','2020-11-01',1),

(2021,'2021-03-14','2021-11-07',1),

(2022,'2022-03-13','2022-11-06',1),

(2023,'2023-03-12','2023-11-05',1),

(2024,'2024-03-10','2024-11-03',1),

(2025,'2025-03-09','2025-11-02',1)

Now JOIN to this table

LEFT JOIN Daylightsavings dst ON

<somedatevalue> between dst.begin and dst.end

Then use isnull

somedatevalue = dateadd(hh,isnull(dst.dst_diff,0),somedatevalue)