explain analyze 
select * from t1 
 where f1 between current_timestamp and current_date::timestamp with time zone + '1 day - 1 second';
                                                                             QUERY PLAN                                                                         
---------------------------------------------------------------------------------------------------------------------------------------------------------------------
 Index Scan using idx on t1  (cost=0.01..8.39 rows=1 width=8) (actual time=0.579..1.632 rows=341 loops=1)
   Index Cond: ((f1 >= (('now'::text)::date)::timestamp with time zone) AND (f1 <= ((('now'::text)::date)::timestamp with time zone + '1 day -00:00:01'::interval)))
 Total runtime: 1.856 ms
(3 rows)