All I have is this quote from Axis Historical Factbook which shows Kempf taking command on 10 Aug. 1939. I've never been really sure on what date this unit was "officially" formed.
Panzer-Division Kempf (aka Panzerverband Ostpreußen) was formed Aug 1939 from a mix of Heer and SS-Verfügungstruppe units in East Prussia, officially to take part in the upcoming Tannenberg celebrations (to celebrate the large German victory there during the First World War).
It took part in the invasion of Poland, fighting at Mlava, Rozan, Lomza, Kliczym and Modlin. It was disbanded following that campaign and the farewell parade was held 7 Oct 1939 near Neidenburg.
Generalmajor Werner Kempf (10 Aug 1939 - ? Oct 1939)
I'm sure somebody here should have the exact date.
(Hello Dr. N. - are you out there?
best regards -