SQL & PL/SQL

Oracle DB 12c

I have a table with a DATE column (among others). I want to select rows just by comparing time portion.

I tried the following but neither gave me correct result (working_start_time is the DATE column)

select to_char(working_start_time,'MMDDYYYY HH:MI AM'),a.* from sch_availability a
where working_start_time >= to_date('08:00 AM','HH:MI AM');


select to_char(working_start_time,'MMDDYYYY HH:MI AM'),a.* from sch_availability a
where to_char(working_start_time,'HH:MI AM') >= '08:00 AM';

So how do I find all rows where time is greater than 8 AM (regardless of date)?