what is the {start time} for {Nancy Reagan} has {spouse} as {Ronald Reagan} ?
At what time did Nancy Reagan marry to Ronald Reagan?
When was Nancy Reagan married to Ronald Reagan?
SELECT ?q WHERE { ?w property:spouse resource:Ronald_Reagan . ?w property:start_time ?q . resource:Nancy_Reagan property:spouse ?w }
select distinct ?value  where {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> <http://wikidata.dbpedia.org/resource/Q193426> .
?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/Q9960> .
?statement <http://www.wikidata.org/entity/P580> ?value. 
} 

SELECT ?value WHERE { wd:Q193426 p:P26 ?s . ?s ps:P26 wd:Q9960 . ?s pq:P580 ?value}