SQL> ed
Wrote file afiedt.buf

  1* select sysdate, to_char(sysdate,'hh24:mi') time from dual
SQL> /

SYSDATE   TIME
--------- -----
18-OCT-02 08:45

select *
  from t
 where to_date(to_char(:vbdate, 'mm/dd/yyyy') || ' ' || :vbtime, 'mm/dd/yyyy hh24:mi') 
   between to_date(to_char(a_date, 'mm/dd/yyyy') || ' ' || a_time, 'mm/dd/yyyy hh24:mi')
       and to_date(to_char(b_date, 'mm/dd/yyyy') || ' ' || b_time, 'mm/dd/yyyy hh24:mi');