Oracle 18c

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with tests as 
    (
    select
        'TEST 1'  as code,
        99999999 as frequency,
        sysdate as last_run
    from dual
        union
    select
        'TEST 2'  as code,
        99999999999 as frequency,
        sysdate as last_run
    from dual
    )
select
    p.*,
    (p.last_run + p.frequency / 24 / 60 ) as next_run
from tests p
where (p.last_run + p.frequency / 24 / 60 < sysdate or p.last_run is null)


CODE
FREQUENCY
LAST_RUN
NEXT_RUN


TEST 2
99999999999
06-FEB-24
12-JUL-52


alter session set nls_date_format = 'DD-MON-YYYY HH:MI:SS AM';
with tests as 
    (
    select
        'TEST 1'  as code,
        99999999 as frequency,
        sysdate as last_run
    from dual
        union
    select
        'TEST 2'  as code,
        99999999999 as frequency,
        sysdate as last_run
    from dual
    )
select
    p.*,
    (p.last_run + p.frequency / 24 / 60 ) as next_run
from tests p
where (p.last_run + p.frequency / 24 / 60 < sysdate or p.last_run is null)


CODE
FREQUENCY
LAST_RUN
NEXT_RUN


TEST 2
99999999999
06-FEB-2024 09:52:31 AM
12-JUL-4452 08:31:31 PM


alter session set nls_date_format = 'SYYYY-MM-DD HH24:MI:SS';
with tests as 
    (
    select
        'TEST 1'  as code,
        99999999 as frequency,
        sysdate as last_run
    from dual
        union
    select
        'TEST 2'  as code,
        99999999999 as frequency,
        sysdate as last_run
    from dual
    )
select
    p.*,
    (p.last_run + p.frequency / 24 / 60 ) as next_run
from tests p
where (p.last_run + p.frequency / 24 / 60 < sysdate or p.last_run is null)


CODE
FREQUENCY
LAST_RUN
NEXT_RUN


TEST 2
99999999999
 2024-02-06 09:52:31
-4452-07-12 20:31:31


with tests as 
    (
    select
        'TEST 1'  as code,
        99999999 as frequency,
        sysdate as last_run
    from dual
        union
    select
        'TEST 2'  as code,
        9999999999 as frequency, -- one digit less
        sysdate as last_run
    from dual
    )
select
    p.*,
    (p.last_run + p.frequency / 24 / 60 ) as next_run
from tests p
where (p.last_run + p.frequency / 24 / 60 < sysdate or p.last_run is null)
ORA-01841: (full) year must be between -4713 and +9999, and not be 0