what is the {start time} for {John von Neumann} has {spouse} as {Klara Dan von Neumann} ?
When did John von Neumann and Kara Dan von Neumann get married?
When did John von Neumann take Kara Dan von Neumann as his spouse?
SELECT ?a WHERE { ?m property:start_time ?a . resource:John_von_Neumann property:spouse ?m . ?m property:spouse resource:Klara_Dan_von_Neumann }
select distinct ?value  where {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> <http://wikidata.dbpedia.org/resource/Q17455> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate> <http://www.wikidata.org/entity/P26> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> <http://wikidata.dbpedia.org/resource/Q14100> .
?statement <http://www.wikidata.org/entity/P580> ?value. 
} 

SELECT ?value WHERE { wd:Q17455 p:P26 ?s . ?s ps:P26 wd:Q14100 . ?s pq:P580 ?value}