PREFIX :       <http://example/>
PREFIX xsd:     <http://www.w3.org/2001/XMLSchema#>

:s :p :o {| :source [ :graph <http://host1/> ;
                      :date "2020-01-20"^^xsd:date
                    ] ;
            :source [ :graph <http://host2/> ;
                      :date "2020-12-31"^^xsd:date
                    ]
          |} .