SQL Server 2017

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.

drop table if exists #tbl
create table #tbl(id int, dt datetime )

insert into #tbl
values
( 1, '2019-11-20 15:30:00.000'),
( 2, '2019-11-20 15:32:00.000'),
( 3, '2019-11-20 15:34:00.000'),
( 4, '2019-11-20 15:45:00.000'),
( 4, '2019-11-20 15:37:00.000'),
( 5, '2019-11-20 15:43:00.000'),
( 6, '2019-11-20 15:46:00.000'),
( 7, '2019-11-20 15:49:30.000'),
( 8, '2019-11-20 15:55:00.000'),
( 9, '2019-11-20 15:58:00.000'),
(10, '2019-11-20 16:01:00.000');

select id, dt from #tbl


id
dt


1
20/11/2019 15:30:00

2
20/11/2019 15:32:00

3
20/11/2019 15:34:00

4
20/11/2019 15:45:00

4
20/11/2019 15:37:00

5
20/11/2019 15:43:00

6
20/11/2019 15:46:00

7
20/11/2019 15:49:30

8
20/11/2019 15:55:00

9
20/11/2019 15:58:00

10
20/11/2019 16:01:00


select min(b.ndt) as dts, 
       iif(max(b.ndt) = max(max(b.ndt)) over() and count(*) = 1, 
           null, 
           max(b.ndt)) as dte
from (select a.id, a.dts, a.dte, a.r, a.ndt, a.v,
             row_number() over(partition by a.r order by a.ndt, a.v) as n
from (select q.id, q.dts, q.dte,
             X.v, 
             u.ndt,
             sum(X.v) over(order by u.ndt desc, X.v desc) as r
from (select t.id, t.dt as dts, 
             dateadd(Minute, 5, t.dt) as dte
        from #tbl as t) as q
       cross join(values (0), (1)) as X(v)
       cross apply(select iif(X.v = 0, q.dts, q.dte) as ndt) as u) as a) as b
where b.v = 0
group by b.r

order by min(b.ndt)



dts
dte


20/11/2019 15:30:00
20/11/2019 15:34:00

20/11/2019 15:37:00
20/11/2019 15:37:00

20/11/2019 15:43:00
20/11/2019 15:46:00

20/11/2019 15:49:30
20/11/2019 15:49:30

20/11/2019 15:55:00
20/11/2019 15:58:00

20/11/2019 16:01:00
null


select min(l.dt), t.dt1
  from #tbl l
 outer apply(select max(x.dt) dt1
               from #tbl x
              where x.dt between l.dt and dateadd(minute,5,l.dt)) t
 group by t.dt1


(No column name)
dt1


20/11/2019 15:30:00
20/11/2019 15:34:00

20/11/2019 15:32:00
20/11/2019 15:37:00

20/11/2019 15:43:00
20/11/2019 15:46:00

20/11/2019 15:45:00
20/11/2019 15:49:30

20/11/2019 15:55:00
20/11/2019 15:58:00

20/11/2019 15:58:00
20/11/2019 16:01:00

id	dt
1	20/11/2019 15:30:00
2	20/11/2019 15:32:00
3	20/11/2019 15:34:00
4	20/11/2019 15:45:00
4	20/11/2019 15:37:00
5	20/11/2019 15:43:00
6	20/11/2019 15:46:00
7	20/11/2019 15:49:30
8	20/11/2019 15:55:00
9	20/11/2019 15:58:00
10	20/11/2019 16:01:00