How often does the Impala StateStore refresh?
It is my understanding that impala does not automatically refresh the metadata.  If you create new tables etc through impala (1.2 and higher) it will update the other impala nodes, however if you create new tables etc in hive you will have to manually refresh the impala metadata.  

You can manually refresh the metadata on either a table basis with 'REFRESH table_name' or you can do this for all tables with 'INVALIDATE METADATA'.  Also, note that if you update the files on HDFS you will have to refresh the table to pickup the new data as well.