How to calculate total time from date column in Oracle

I have a table where i have some log like this.

select table_name,  
    min(to_char(DATO,'dd.mm.yyyy hh24:mi')) as start_time, 
    max(to_char(DATO,'dd.mm.yyyy hh24:mi')) as end_time
from TMP_AUDIT_LOG t
where FLAG='Y'
and TR_MODE='EXPORT'
group by T.TABLE_NAME
order by 2

and output is like below

TABLE_NAME  START_TIME          END_TIME
----------  ----------------    ----------------
MAPTEXT     06.11.2020 17:29    06.11.2020 18:12
COMPONENT   06.11.2020 18:12    06.11.2020 19:18
SETTKONT    06.11.2020 19:18    06.11.2020 20:24
ROUTELOG    06.11.2020 20:24    06.11.2020 20:44
CROSSEC     06.11.2020 20:44    06.11.2020 20:49

But I want to have one more column which will give me total time like below

TABLE_NAME  START_TIME          END_TIME          TOTAL_TIME
----------  ----------------    ----------------  ----------
MAPTEXT     06.11.2020 17:29    06.11.2020 18:12  43m
COMPONENT   06.11.2020 18:12    06.11.2020 19:18  1h 6m
SETTKONT    06.11.2020 19:18    06.11.2020 20:24  1h 6m
ROUTELOG    06.11.2020 20:24    06.11.2020 20:44  24m
CROSSEC     06.11.2020 20:44    06.11.2020 20:49  5m

I have tried to minus both time but not getting proper result.

select table_name, start_time, end_time, 
(to_date(end_time,'dd.mm.yyyy hh24:mi')-to_date(start_time,'dd.mm.yyyy hh24:mi')) as total_time from (
select table_name,  
  min(to_char(DATO,'dd.mm.yyyy hh24:mi')) as start_time, 
  max(to_char(DATO,'dd.mm.yyyy hh24:mi')) as end_time
from TMP_EXPORT_WORKSPACE t
where FLAG='Y'
and TR_MODE='EXPORT'
group by T.TABLE_NAME
order by 2
)
;

The output i am getting is below

TABLE_NAME  START_TIME          END_TIME          TOTAL_TIME
----------  ----------------    ----------------  ----------
MAPTEXT     06.11.2020 17:29    06.11.2020 18:12  0.0298611111111111111111111111111111111111
COMPONENT   06.11.2020 18:12    06.11.2020 19:18  0.0458333333333333333333333333333333333333
SETTKONT    06.11.2020 19:18    06.11.2020 20:24  0.0458333333333333333333333333333333333333
ROUTELOG    06.11.2020 20:24    06.11.2020 20:44  0.0138888888888888888888888888888888888889
CROSSEC     06.11.2020 20:44    06.11.2020 20:49  0.003472222222222222222222222222222222222222

Answer

Don’t convert the dates to strings. That makes no sense and only leads to unexpected results. The column dato is a DATE and per table you want the minimum dato and the maximum dato, so just use MIN(dato) and MAX(dato). Then you want the difference. You get the difference by subtracting one from the other:

select
  table_name,  
  min(dato) as start_time, 
  max(dato) as end_time,
  max(dato) - min(dato) as total_time
from tmp_audit_log t
where flag = 'Y'
and tr_mode = 'EXPORT'
group by table_name
order by start_time;

As dato is a DATE, you get the difference as a fraction of days. If you want an INTERVAL instead, convert from DATE to TIMESTAMP:

max(cast(dato as timestamp)) - min(cast(dato as timestamp)) as total_time