SELECT * FROM your_table WHERE CAST(EXTRACT(DAY FROM your_date_column) AS int)% 2 = 0 ;

wsdb=# SELECT CAST(EXTRACT(DAY FROM TIMESTAMP '2001-02-12 20:38:40') as int)% 2 ;
 ?column? 
----------
         0 
( 1  row)

wsdb=# SELECT CAST(EXTRACT(DAY FROM TIMESTAMP '2001-02-15 20:38:40') as int)% 2 ;
 ?column? 
----------
         1 
( 1  row)

wsdb=# SELECT CAST(EXTRACT(DAY FROM TIMESTAMP '2001-02-18 20:38:40') as int)% 2 ;
 ?column? 
----------
         0 
( 1  row)