Yes, it is a very good idea. Some big companies expect you to respond to their calls at any time of the day. My friends in US are really struggling working for such companies. I have a Korean friend who works for a big company on the west coast of US. He goes to work at 7 am and comes back at around 5 pm. Sleeps for a couple of hours and then works again from home until around 1-2 am. He is getting paid for 8 hours of work and so much work is expected from him.
So, such constraints on these greedy companies are really good. They can then no longer exploit their employees and they can have a life outside of their work. I applaud Germany for taking such a bold step.
And, for the people who are saying that they need to interact with people in other timezones, different 8 hour time-slots should be assigned to employees and they should not be expected to work more than 8 hours. It is really easy to implement. The companies use the timezone "ploy" to extract more hours of work from their employees.