I too have to leave for work at 6. So i walk mine before i go, in the dark, with a torch. If i dont do this, my GSD becomes destructive.
I can then leave him with his dinner scattered around the garden. Meat stock frozen inside safe plastic bottle throw aways, a digging pit, with some more dinner hidden there.
Treat balls take a GSD a moment. Garden collection of dinner takes a lot longer.
Water, most GSD's lurve to get into a puddle, river, sea, you name it. Get one of those turtle shells, and fill half of this with water. Put toys under the water
you could consider rethinking your decision, to get a GSD.
It seems to me, a serial GSD owner, that what you want from a dog, and are prepared to give, would be better suited to say a bordeaux mastiff, than a GSD. The reason im seeing a mismatch of needs, is that GSD's are not really outside dogs. They are herders, they must have what they gaurd in sight. In order to relax, and be happy. They must have 'jobs to do', or they get into mischief. And with those teeth, that's a lot of mischief.
If you are willing to accept, that currently, you and your dogs needs are not in synch, are you willing to change into the owner you need to be, for one of these dogs, or rehome him, learn a lesson, and chose wisely next time around with hindsight?