What do these stage directions reveal about when the opening scene takes place ?

It takes place after the Franks have been captured.

Explanation:

The Franks and the others hiding in the Secret Annex were caught by the Gestapo, on August 4, 1944, and sent to concentration camps. The curtains in rags and furniture overturned seem to reflect that that event has already happened.

Otto, Anne Frank’s father, was the only one who survived and was freed from Auschwitz by Soviet troops on January 27, 1945.