Oracle 18c

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CREATE TABLE db (ID, UnixDateTime, OrderNumber) AS
SELECT 1, 1662615688, 100 FROM DUAL UNION ALL
SELECT 2, 1662615752, 100 FROM DUAL UNION ALL
SELECT 3, 1662615765, 100 FROM DUAL UNION ALL
SELECT 4, 1662615859, 100 FROM DUAL UNION ALL
SELECT 5, 1662615987, 100 FROM DUAL UNION ALL
SELECT 6, 1662616031, 100 FROM DUAL;
6 rows affected

ALTER SESSION SET NLS_TIMESTAMP_TZ_FORMAT = 'YYYY-MM-DD HH24:MI:SS.FF TZR';
SELECT id,
       unixdatetime,
       ordernumber,
       date_time,
       next_unixdatetime,
       next_unixdatetime - unixdatetime AS diff,
       CASE cls
       WHEN 'WITHIN_100' THEN 1
       ELSE 0
       END AS within_100
from   (
  select distinct 
         ID,
         UnixDateTime,
         OrderNumber,
         TIMESTAMP '1970-01-01 00:00:00 UTC' + UnixDateTime * INTERVAL '1' SECOND
           AS Date_Time
  from   DB
  where  TIMESTAMP '1970-01-01 00:00:00 UTC' + UnixDateTime * INTERVAL '1' SECOND
           > SYSTIMESTAMP - INTERVAL '2' DAY
)
MATCH_RECOGNIZE(
  ORDER BY unixdatetime
  MEASURES
    NEXT(unixdatetime) AS next_unixdatetime,
    classifier() AS cls
  ALL ROWS PER MATCH
  PATTERN (within_100* any_row $)
  DEFINE
    within_100 AS NEXT(unixdatetime) < unixdatetime + 100
) m


ID
UNIXDATETIME
ORDERNUMBER
DATE_TIME
NEXT_UNIXDATETIME
DIFF
WITHIN_100


5
1662615987
100
2022-09-08 05:46:27.000000000 UTC
1662616031
44
1

6
1662616031
100
2022-09-08 05:47:11.000000000 UTC
null
null
0

ID	UNIXDATETIME	ORDERNUMBER	DATE_TIME	NEXT_UNIXDATETIME	DIFF	WITHIN_100
5	1662615987	100	2022-09-08 05:46:27.000000000 UTC	1662616031	44	1
6	1662616031	100	2022-09-08 05:47:11.000000000 UTC	null	null	0