Anyone see one of these before and what is it used for?

Was it a converted CDIA to a Rally timer?

The dial markings are 24 hours, 60 minutes and 100 Centi-minutes (0.01 minutes) probably intended for navigation and fuel burn calculations.

It is a CDIA case, and your guess that it might have been a later conversion by the BBS company of Germany to a auto rally timer clock makes sense to me. There is a BBS company in Germany that makes after sale auto parts - I don't know if it the same BBS as the sticker on the back of this clock though. It would have been a lower cost option than using the British aircraft chronos that were commonly recycled by auto rally participants after the war.