How to get previous N rows for multiple joining rows

I am writing a SQL with Oracle Client 12 driver. I have two tables simplified as appended, and I want to get a table with following logic. The "B.TIME_B <= A0.TIME_A" seems created massive joining and made the query very slow. Please help to find best solution.

WITH A0 AS (
  SELECT *
  FROM A
  WHERE A.EVENT = 'a0'
)

SELECT * FROM (
SELECT
  ROW_NUMBER() OVER (PARTITION BY A0.TIME_A0 ORDER BY B.TIME_B DESC) RN, 
  A0.*,
  B.*
FROM 
   A0,B
WHERE
   B.TIME_B <= A0.TIME_A) B0

WHERE B0.RN <= 3   

1. Find TIME_A, where EVENT_A = 'a0', as TIME_A0,

2. Find TIME_B = TIME_A0, as EVENT_B0,

3. And then get the row and previous 2 rows of table B, where EVENT_B0 found. N in this example is 3, and M is 2, but in real case both number are over 3000, so efficiency will be appreciated.

TableA

TIME_A  EVENT_A
1       a1
2       a1
3       a1
4       a0
5       a2
6       a2
7       a3
8       a0

Table B

TIME_B  EVENT_B
1       b1
2       b2
3       b3
4       b4
5       b5
6       b5
7       b6
8       b7

JOIN A_B

TIME_A  EVENT_A TIME_B  EVENT_B
4       a0      2       b2
4       a0      3       b3
4       a0      4       b4
8       a0      6       b5
8       a0      7       b6
8       a0      8       b7

Query 1:

If you are not going to have overlapping ranges then you can use:

SELECT *
FROM   (
  SELECT TIME_B,
         EVENT_B,
         MAX( TIME_A  ) OVER ( ORDER BY TIME_B ROWS BETWEEN CURRENT ROW AND 2 FOLLOWING )
           AS TIME_A,
         MAX( EVENT_A ) OVER ( ORDER BY TIME_B ROWS BETWEEN CURRENT ROW AND 2 FOLLOWING )
           AS EVENT_A
  FROM   tableB B
         LEFT OUTER JOIN tableA A
         ON ( B.TIME_B = A.TIME_A AND A.EVENT_A = 'a0' )
)
WHERE  TIME_A IS NOT NULL;

Which only uses a single join and then finds the valid rows with analytic functions.

Output:

TIME_B | EVENT_B | TIME_A | EVENT_A
-----: | :------ | -----: | :------
     2 | b2      |      4 | a0     
     3 | b3      |      4 | a0     
     4 | b4      |      4 | a0     
     6 | b5      |      8 | a0     
     7 | b6      |      8 | a0     
     8 | b7      |      8 | a0     

db<>fiddle here

---

Query 2:

If you could have overlapping ranges then you could use a hierarchical query to generate the rows:

SELECT TIME_B,
       EVENT_B,
       CONNECT_BY_ROOT( TIME_A ) AS TIME_A,
       CONNECT_BY_ROOT( EVENT_A ) AS EVENT_A
FROM   (
  SELECT A.*,
         B.*,
         ROW_NUMBER() OVER ( ORDER BY TIME_B ) AS rn
  FROM   tableB B
         LEFT OUTER JOIN tableA A
         ON ( B.TIME_B = A.TIME_A AND A.EVENT_A = 'a0' )
)
WHERE LEVEL <= 2
START WITH EVENT_A IS NOT NULL
CONNECT BY PRIOR rn -2 <= rn AND rn < PRIOR rn
ORDER BY time_a, time_b

Output:

TIME_B | EVENT_B | TIME_A | EVENT_A
-----: | :------ | -----: | :------
     2 | b2      |      4 | a0     
     3 | b3      |      4 | a0     
     4 | b4      |      4 | a0     
     6 | b5      |      8 | a0     
     7 | b6      |      8 | a0     
     8 | b7      |      8 | a0     
     8 | b7      |     10 | a0     
     9 | b8      |     10 | a0     
    10 | b9      |     10 | a0     

db<>fiddle here