what is the {start time} for {Seoul} has {twinned administrative body} as {Tokyo} ?
What date did Seoul become a sister city with Tokyo?
When did Seoul become a sister city with Tokyo?
SELECT ?b WHERE { ?i property:twinned_administrative_body resource:Tokyo . ?i property:start_time ?b . resource:Seoul property:twinned_administrative_body ?i }
select distinct ?value  where {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> <http://wikidata.dbpedia.org/resource/Q8684> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate> <http://www.wikidata.org/entity/P190> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> <http://wikidata.dbpedia.org/resource/Q1490> .
?statement <http://www.wikidata.org/entity/P580> ?value. 
} 

SELECT ?value WHERE { wd:Q8684 p:P190 ?s . ?s ps:P190 wd:Q1490 . ?s pq:P580 ?value}