what is the {start time} for {Bibi Andersson} has {spouse} as {Per Ahlmark} ?
When did the wedding of Bibi Andersson to Per Ahlmark take place?
When was Bibi Andersson married to Per Ahlmark?
SELECT ?x WHERE { resource:Bibi_Andersson property:spouse ?y . ?y property:start_time ?x . ?y property:spouse resource:Per_Ahlmark }
select distinct ?value  where {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> <http://wikidata.dbpedia.org/resource/Q234921> .
?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/Q1347731> .
?statement <http://www.wikidata.org/entity/P580> ?value. 
} 

SELECT ?value WHERE { wd:Q234921 p:P26 ?s . ?s ps:P26 wd:Q1347731 . ?s pq:P580 ?value}