what is the {start time} for {William Herschel} has {position held} as {President of the Royal Astronomical Society} ?
What was the date when William Herschel began his term as the President of the Royal Astronomical Society?
When did WIlliam Herschel started to serve as President of the Royal Astronomical Society?
SELECT ?k WHERE { ?t property:start_time ?k . resource:William_Herschel property:position_held ?t . ?t property:position_held resource:President_of_the_Royal_Astronomical_Society }
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?statement <http://www.wikidata.org/entity/P580> ?value. 
} 

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