It is not clear if you're using two tables - a source and a destination table, or you simply want to select the time element from timestamp datatype from a single table.
Extracting the time from a timestamp involves extracting the different components in the timestamp, for example:
select concat(hour(current_timestamp()), ':', minute(current_timestamp()), ':', second(current_timestamp()));
** https://cwiki.apache.org/confluence/display/Hive/LanguageManual+UDF#LanguageManualUDF-DateFunctions