Comment by netsharc

I can imagine the systems were rickety that it was more convenient to have routine maintenance hours. Routine in the sense of "We just need to wait until tonight to fix the problem", rather than "We need to fix this, we have to apply for a maintenance period, wait for it to be announced to the customers, etc, etc."

Since it's Germany it'd have to go through to many departments and take at least a week to be approved.