select wonum, description, targcompdate from workorder
where 
(DATE('15-MAY-08')-targcompdate >=90)
and 
status
in (
    'INPRG',
    'WSCH'
    )
and
istask ='0'
and
worktype = 'PM'
ORDER BY TARGCOMPDATE

SQL> select to_date('15-may-08') from dual;
select to_date('15-may-08') from dual
               *
ERROR at line 1:
ORA-01858: a non-numeric character was found where a numeric was expected

SQL> select to_date('15-may-08', 'dd-mon-yy') from dual;
select to_date('15-may-08', 'dd-mon-yy') from dual
               *
ERROR at line 1:
ORA-01843: not a valid month

SQL> select to_date('15-may-08', 'dd-mon-yy', 'nls_date_language=english')
  2  from dual;

TO_DATE(
--------
15.05.08

SQL>

Const strFirstPart As String = "select count(*) from maximo.workorder where (TO_DATE('"
Const strLastPart As String = "')-workorder.targcompdate >=90) and workorder.Status in ('INPRG','WSCH) and workorder.istask ='0' and workorder.worktype = 'PM'"
 
'ASSUMING INPUT CELL HAS DATE TEXT IN CORRECT FORMAT - recommend that this is tested in the code.
Debug.Print strFirstPart & Range("A1").Value & strLastPart