Simple example of how smart is Oracle CBO with indexes like on dates(trunc(date_col))

1.output.sql

SQL> create table dates(date_col, padding) as select date'2020-01-01' + level*5/24/60, level from dual connect by level<=10000;
SQL> create index ix_dates_trunc on dates(trunc(date_col));
SQL> exec dbms_stats.gather_table_stats('','DATES');
SQL> select min(date_col),max(date_col),count(*) from dates where date_col=to_date('2020-01-15 01:15','yyyy-mm-dd hh24:mi');

MIN(DATE_COL)       MAX(DATE_COL)         COUNT(*)
------------------- ------------------- ----------
2020-01-15 01:15:00 2020-01-15 01:15:00          1
SQL> select * from dbms_xplan.display_cursor('','','allstats last -projection -alias');

PLAN_TABLE_OUTPUT
-----------------------------------------------------------------------------------------------------------------
SQL_ID  fd6supjf60v5q, child number 0
-------------------------------------
select min(date_col),max(date_col),count(*) from dates where
date_col=to_date('2020-01-15 01:15','yyyy-mm-dd hh24:mi')

Plan hash value: 3740522312

-----------------------------------------------------------------------------------------------------------------
| Id  | Operation                            | Name           | Starts | E-Rows | A-Rows |   A-Time   | Buffers |
-----------------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                     |                |      1 |        |      1 |00:00:00.01 |       5 |
|   1 |  SORT AGGREGATE                      |                |      1 |      1 |      1 |00:00:00.01 |       5 |
|*  2 |   TABLE ACCESS BY INDEX ROWID BATCHED| DATES          |      1 |      1 |      1 |00:00:00.01 |       5 |
|*  3 |    INDEX RANGE SCAN                  | IX_DATES_TRUNC |      1 |     40 |    288 |00:00:00.01 |       3 |
-----------------------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   2 - filter("DATE_COL"=TO_DATE(' 2020-01-15 01:15:00', 'syyyy-mm-dd hh24:mi:ss'))
   3 - access("DATES"."SYS_NC00003$"=TRUNC(TO_DATE(' 2020-01-15 01:15:00', 'syyyy-mm-dd hh24:mi:ss')))

2.test.sql

create table dates(date_col, padding) as select date'2020-01-01' + level*5/24/60, level from dual connect by level<=10000;
create index ix_dates_trunc on dates(trunc(date_col));
exec dbms_stats.gather_table_stats('','DATES');
select min(date_col),max(date_col),count(*) from dates where date_col=to_date('2020-01-15 01:15','yyyy-mm-dd hh24:mi');
select * from dbms_xplan.display_cursor('','','allstats last -projection -alias');