Oracle 18c

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with tests as (
    select 'TEST 1'  as code, 99999999 as frequency, sysdate as last_run
    from dual union all
    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
08-OCT-21
14-MAR-54


alter session set nls_date_format = 'DD-MON-YYYY HH24:MI:SS';
with tests as (
    select 'TEST 1'  as code, 99999999 as frequency, sysdate as last_run
    from dual union all
    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
08-OCT-2021 10:44:02
14-MAR-4454 21:23:02


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 all
    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
 2021-10-08 10:44:02
-4454-03-14 21:23:02


with tests as (
    select 'TEST 1'  as code, 99999999 as frequency, sysdate as last_run
    from dual union all
    select 'TEST 2'  as code, 9999999999 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)
ORA-01841: (full) year must be between -4713 and +9999, and not be 0