what is the {start time} for {Niue} has {member of} as {United Nations Educational, Scientific and Cultural Organization} ?
What date did Niue become a member of the UNESCO?
When did Niue become a member of the United Nations Educational, Scientific and Cultural Organization?
SELECT ?k WHERE { ?z property:start_time ?k . ?z property:member_of resource:UNESCO . resource:Niue property:member_of ?z }
select distinct ?value  where {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> <http://wikidata.dbpedia.org/resource/Q34020> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate> <http://www.wikidata.org/entity/P463> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> <http://wikidata.dbpedia.org/resource/Q7809> .
?statement <http://www.wikidata.org/entity/P580> ?value. 
} 

SELECT ?value WHERE { wd:Q34020 p:P463 ?s . ?s ps:P463 wd:Q7809 . ?s pq:P580 ?value}