expdp - dump until certain date

I want to export a schema using expdp until certain date. I managed to fully export the schema.

Now I want to export the same thing but until 30th April 2014. I used

query="where datetime_stamp <= (sysdate-14)"

But I'm getting error

LRM-00101: unknown parameter name '<'

here is the full commnand.

expdp system/blabla schemas=bla_blah DIRECTORY=expdp_dir DUMPFILE=blabla_DB.dmp LOGFILE=expfull_DB.log query="where datetime_stamp <= (sysdate-14)"

Note that if I remove starting with query... I managed to export full schema. But now I want until 30th April 2014. Thanks.