Try:

Select *
from table
where date_field >= trunc(sysdate-1) + interval '17' hour
  and date_field < trunc(sysdate) + interval '8' hour;

I have assumed that you actually want to run the report for activity happening between 17:00 inclusive and 08:00 exclusive, in which case you should not use BETWEEN. If you want to include activities that happened exactly at 08:00:00 as well, then BETWEEN is fine. The above condition does some implicit conversions between DATE and TIMESTAMP but they are cheaper than conversions between DATE and VARCHAR2.

Your attempt has a couple of errors. You rely on implicit conversion of the TRUNC result to VARCHAR2 before concatenating it with the hour string. This makes the result dependent on NLS_DATE_FORMAT session parameter. Also, you use HH instead of HH24. The version of the query that uses VARCHAR2 as intermediate form should like this:

Select *
from table
where date_field >= to_date(to_char(sysdate-1,'YYYYMMDD')||'17:00','YYYYMMDDHH24:MI')
  and date_field <  to_date(to_char(sysdate,'YYYYMMDD')||'08:00','YYYYMMDDHH24:MI');

Note that TRUNC is not needed here as we can truncate the time portion simply by using the appropriate format.