Most of the European city marathons start at 9 or 10 am which means one has to get up quite early. The key reason is that most of us want to eat at least something for breakfast, and secure that the stomach is empty at the starting line. Also it is recommendable to be awake and alert at the start.
It is a good idea to prepare a timetable for the marathon day in advance. It is better for heart and mind to stay calm, instead of wasting energy on stressing around in the morning.
This is a timetable that I used in Berlin, 2011 and which worked well for me:
05:00 - 06:00
A couple of points to the timetable above:
You might want to factor in some more time for arriving at the marathon area and clothes storage if you are unfamiliar with the marathon. Furthermore, you should in advance take note of what the start area looks like, where the clothe storage area is located, and how long it takes from clothes storage to the starting line.
Also it makes sense to book a room at a hotel which is relatively close (1-2 kilometers) to the marathon start since this enables a slow and enjoyable walk to the marathon area.
Finally, the following preparations during the evening before the race help avoiding stress during race morning: