For an import permit they will process it within a week usually.

You are stuck however with finding a hazmat courier, ammunition is a hazardous material when shipped between countries in the EU, and so you will be paying thousands to a hazmat courier to transport ammunition between any EU country.

In short it is not economic for an individual to do so, especially since the larger ammo distributors will not ship to an individual here, only to a dealer because the permit process for them from dealer to dealer is easier.

If you do happen to find a courier who will ship ammo for a reasonable price then do please share it here, but any I have found who are willing to accommodate the request started at a couple grand.

Ammo is allowed on some airlines, up to a total weight of 5kg including packaging, so probably 200 rounds or so of 308.

There is often a charge for it by the airline and you'd need to get the necessary permits on the German side to possess it while there also.