what is the {start time} for {Ali Khamenei} has {position held} as {Supreme Leader of Iran} ?
At what point did Ali Khamenei become Iran's Supreme Leader?
When Ali Khamenei started as Supreme Leader of Iran?
SELECT ?z WHERE { ?h property:position_held resource:Supreme_Leader_of_Iran . resource:Ali_Khamenei property:position_held ?h . ?h property:start_time ?z }
select distinct ?value  where {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> <http://wikidata.dbpedia.org/resource/Q57336> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate> <http://www.wikidata.org/entity/P39> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> <http://wikidata.dbpedia.org/resource/Q332486> .
?statement <http://www.wikidata.org/entity/P580> ?value. 
} 

SELECT ?value WHERE { wd:Q57336 p:P39 ?s . ?s ps:P39 wd:Q332486 . ?s pq:P580 ?value}