SPARQL subquery wtih xsd:dateTime - sparql

Question

I've made one query which returns the date of the Hiroshima bombing.
SELECT ?date
WHERE {
history:the_bombing_of_hiroshima history:hasStartDate ?date .
}
Result: 1945-08-06T:00:00:00
And another query which returns all of the administration that ruled the Soviet Union.
SELECT ?administration
WHERE {
?administration history:rulesCountry "The Soviet Union"^^xsd:string .
}
Now, I'm wondering. An administration in our ontology has a "startDate" and "endDate" data property. Both containing xsd:dateTime values. I want to pass the date, received from the first query into the second query so that we can get the administration that ruled the Soviet Union during the bombing of Hiroshima.
I've tried to read some SPARQL subquery examples but none of them concern dateTime filtering (check to see if a date falls between two others) and many of them are a bit confusing to me.
I suspect the query must be something like
SELECT ?administration
WHERE {
?administration history:rulesCountry "The Soviet Union"^^xsd:string .
?administration history:hasStartDate > [RESULT FROM QUERY1 HERE] && history:hasEndDate < [RESULT FROM QUERY1 HERE]
}
I'd be very grateful for any answers or pointers towards resources and tutorials I can read to get this query to work.