But German officials said three artworks - including Femme Assise by Henri Matisse - would be returned immediately.
A similar agreement was signed last week for the return of a painting by Max Liebermann, Zwei Reiter am Strand [Two Riders on the Beach].
Artworks going home
Henri Matisse's Femme Assise [Seated Woman] was looted from Jewish art dealer Paul Rosenberg and is set to be returned to his descendants, who had been looking for the piece when Gurlitt's hoard was discovered
Max Liebermann's Two Riders on the Beach is said to have been seized from industrialist and avid art collector David Friedmann "as a consequence of the Nazi persecution of Jewish citizens". His great-nephew, David Toren, had taken legal action against Germany for its restitution
Carl Spitzweg's Playing the Piano is to be returned to the heirs of music publisher Henri Hinrichsen, who was murdered at Auschwitz in 1942
Gurlitt's father, Hildebrand Gurlitt, was ordered by Adolf Hitler to deal in works that had been seized from Jewish families, or which the Nazis considered "degenerate" and had been removed from German museums in the 1930s and 1940s.
Matisse's Femme Assise, painted in 1921, was taken from Jewish art dealer Paul Rosenberg in Paris in 1941.
His family had been searching for it until it turned up in Gurlitt's flat.