I flew SLC-Frankfort direct and then Frankfurt to Windhoek direct in 2022. My first flight was delayed a day, and it messed up everything. My new itinerary required a change of airline (Eurowings to Lufthansa), claim and "import" of my rifles at the baggage claim in Frankfurt, and check-in of the rifles a few minutes later at the Lufthansa counter.
Originally, the rifles were supposed to be checked all the way through. Fortunately, I had the Frankfurt transit permit in place, just in case. Without it, my trip would have been a disaster. As it was, it was only 3 short hours of messing around with German police and customs agents. Good thing I had a long layover.
I don't remember exactly how long it took to get the permit, but I'm 100% certain it was longer than a week. Might be time to make some phone call to see if you can make it happen.