use tempdb
GO

CREATE TABLE T (computername VARCHAR(100),currentuser VARCHAR(100), DT datetime, TheOrder INT)
GO



/*************** Viorel-1: test 1 *******************/
TRUNCATE TABLE T
GO
INSERT T(computername, currentuser, DT, TheOrder)
VALUES
('abc', 'xyz', CONVERT(DATETIME,'7/5/2022 20:04:51',101),1),
('abc', 'xyz', CONVERT(DATETIME,'7/5/2022 20:04:51',101),1),
('abc', 'xyz', CONVERT(DATETIME,'7/6/2022 6:45:51',101),1),
('abc', 'xyz', CONVERT(DATETIME,'7/6/2022 6:45:51',101),1),
('abc', 'xyz', CONVERT(DATETIME,'7/6/2022 7:06:45',101),2),
('abc', 'xyz', CONVERT(DATETIME,'7/6/2022 7:06:45',101),3),
('abc', 'xyz', CONVERT(DATETIME,'7/6/2022 7:07:00',101),4),
('abc', 'xyz', CONVERT(DATETIME,'7/6/2022 7:59:12',101),2),
('abc', 'xyz', CONVERT(DATETIME,'7/6/2022 7:59:12',101),3),
('abc', 'xyz', CONVERT(DATETIME,'7/6/2022 7:59:19',101),4),
('abc', 'xyz', CONVERT(DATETIME,'7/6/2022 7:59:21',101),5),
('abc', 'xyz', CONVERT(DATETIME,'7/6/2022 21:28:19',101),1),
('abc', 'xyz', CONVERT(DATETIME,'7/6/2022 21:28:19',101),1),
('abc', 'xyz', CONVERT(DATETIME,'7/6/2022 21:28:24',101),2),
('abc', 'xyz', CONVERT(DATETIME,'7/6/2022 21:28:24',101),3),
('abc', 'xyz', CONVERT(DATETIME,'7/6/2022 21:28:24',101),4)
GO

 ; with Q1 as (
     select *,
         lag([TheOrder]) over (partition by computername, currentuser, cast([DT] as date) order by [DT]) po,
         lead([TheOrder]) over (partition by computername, currentuser, cast([DT] as date) order by [DT]) no
     from T
 ),
 Q2 as (
     select *,
         case when po is null or po > [TheOrder] then [DT] end as starttime,
         case when no is null or [TheOrder] > no then [DT] end as endtime
     from Q1
 ),
 Q3 as (
     select *
     from Q2
     where starttime is not null or endtime is not null
 ),
 Q4 as (
     select computername, currentuser,
         starttime,
         lead(endtime) over (partition by computername, currentuser, cast([DT] as date) order by [DT]) as endtime
     from Q3
 )
 select *
 from Q4
 where starttime is not null
 GO


/*************** Viorel-1: test 2 *******************/
TRUNCATE TABLE T
GO
INSERT T(computername, currentuser, DT, TheOrder)
VALUES
('abc', 'xyz', CONVERT(DATETIME,'7/6/2022 7:07:00',101),4), -- moving this row to the start
('abc', 'xyz', CONVERT(DATETIME,'7/6/2022 7:59:12',101),3), -- moving this ro
('abc', 'xyz', CONVERT(DATETIME,'7/5/2022 20:04:51',101),1),
('abc', 'xyz', CONVERT(DATETIME,'7/5/2022 20:04:51',101),1),
('abc', 'xyz', CONVERT(DATETIME,'7/6/2022 6:45:51',101),1),
('abc', 'xyz', CONVERT(DATETIME,'7/6/2022 6:45:51',101),1),
('abc', 'xyz', CONVERT(DATETIME,'7/6/2022 7:06:45',101),2),
('abc', 'xyz', CONVERT(DATETIME,'7/6/2022 7:06:45',101),3),
('abc', 'xyz', CONVERT(DATETIME,'7/6/2022 7:59:12',101),2),
('abc', 'xyz', CONVERT(DATETIME,'7/6/2022 7:59:19',101),4),
('abc', 'xyz', CONVERT(DATETIME,'7/6/2022 7:59:21',101),5),
('abc', 'xyz', CONVERT(DATETIME,'7/6/2022 21:28:19',101),1),
('abc', 'xyz', CONVERT(DATETIME,'7/6/2022 21:28:19',101),1),
('abc', 'xyz', CONVERT(DATETIME,'7/6/2022 21:28:24',101),2),
('abc', 'xyz', CONVERT(DATETIME,'7/6/2022 21:28:24',101),3),
('abc', 'xyz', CONVERT(DATETIME,'7/6/2022 21:28:24',101),4)
GO

 ; with Q1 as (
     select *,
         lag([TheOrder]) over (partition by computername, currentuser, cast([DT] as date) order by [DT]) po,
         lead([TheOrder]) over (partition by computername, currentuser, cast([DT] as date) order by [DT]) no
     from T
 ),
 Q2 as (
     select *,
         case when po is null or po > [TheOrder] then [DT] end as starttime,
         case when no is null or [TheOrder] > no then [DT] end as endtime
     from Q1
 ),
 Q3 as (
     select *
     from Q2
     where starttime is not null or endtime is not null
 ),
 Q4 as (
     select computername, currentuser,
         starttime,
         lead(endtime) over (partition by computername, currentuser, cast([DT] as date) order by [DT]) as endtime
     from Q3
 )
 select *
 from Q4
 where starttime is not null