Schedules are not important for dog training etc.
The bigger breeds like the rotty you mentioned actually need schedules even less. Why? Well big dogs do much better on one meal per day, digestion is really hard work. The training is a constant thing, not a few minutes per day although that's really what it adds up to. Whenever you're home you train the dog, encouraging what behaviour you want and discouraging the bahaviour you don't. What's not advisable is getting a dog when you know you won't be home most of the time, but getting home later than usual, that sort of thing is perfectly fine.
You can also feed your dog before you leave if you have no idea how long it'll take to finish some work.
Daily walks are flexible depending on the work out the dog is able to get at home, I have a big yard on a busy road which means my dogs have plenty of work to do encouraging people to walk on the other side of the road.
They have a big park to run around in just up the road as well so these 2 things together is what keeps my dogs looking exceptionally healthy.
Lastly relaxing rules for small breeds is what makes them so menacing, if you have rules the dog should abide by them regardless of how small and tame and harmless you might think it is.