Can the overnight trains be accessed 24hrs a day? So if we wanted to leave a city at 11pm and arrive at a different city at 8am the next day. Is that possible? Also do the high speed trains still stop along the way? how long will they stop for, if so? Will we be able to get off the train and explore a little? Thank you!
Overnight trains: it depends on your point of origin and destination.
High speed trains: They stop just for short time for people to get off and on. If you want to explore you get off and then board another train. You can check schedule and more on Deutsche Bahn website. They have schedule for all Europe.
Reserved seats are required on high-speed trains and come with the ticket. If you want to get off for a few hours somewhere between point A and point B, you'll have to book two separate tickets, one for each portion of the route.
There are just a few night trains on certain routes, and you will have to stick to whatever timetable there is. As for high-speed trains: they call at stations just for a couple minutes, sometimes (big exceptions) up to 12 minutes but no more than that!
Courtney, it would be very helpful if you said which city you want to leave at 11pm, and what town you would like to arrive in at 8 am. There are only a few actual night trains and they run when they run. I completely don't understand your question Can the overnight trains be accessed 24hrs a day? You can only get on overnight trains when they are in the city you are leaving from and that is at night. Not all combinations of cities are served by high speed trains either. Again, it would be really helpful if you would say which cities. You haven't even said which countries.