what is the {start time} for {David Cameron} has {position held} as {First Lord of the Treasury} ?
When did David Cameron take over as First Lord of the Treasury?
When did David Cameron, First Lord of the Treasury, begin his position?
SELECT ?p WHERE { ?j property:start_time ?p . resource:David_Cameron property:position_held ?j . ?j property:position_held resource:First_Lord_of_the_Treasury }
select distinct ?value  where {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> <http://wikidata.dbpedia.org/resource/Q192> .
?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/Q609884> .
?statement <http://www.wikidata.org/entity/P580> ?value. 
} 

SELECT ?value WHERE { wd:Q192 p:P39 ?s . ?s ps:P39 wd:Q609884 . ?s pq:P580 ?value}