what is the {start time} for {Keith Holyoake} has {position held} as {Prime Minister of New Zealand} ?
What year did Keith Holyoake become the Prime Minister of New Zealand?
When did Keith Holyoake become the Prime Minister of New Zealand?
SELECT ?v WHERE { ?s property:start_time ?v . resource:Keith_Holyoake property:position_held ?s . ?s property:position_held resource:Prime_Minister_of_New_Zealand }
select distinct ?value  where {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> <http://wikidata.dbpedia.org/resource/Q637012> .
?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/Q1071117> .
?statement <http://www.wikidata.org/entity/P580> ?value. 
} 

SELECT ?value WHERE { wd:Q637012 p:P39 ?s . ?s ps:P39 wd:Q1071117 . ?s pq:P580 ?value}