Of course you should add the correct one. 

But there's no need to do it in advance. Just add the next one when being at the platform. So it should be no problem to add the correct one.

But most of the time you'd have no control anyway. And there's a chance that nobody cares even if there is a check of your ticket. 

Thanks for the quick response Yes I know I should, it just feels a bit rushed to find and add the right one so that’s why I was wondering… Since they leave so often I find it a bit fiddly to add the the time, find the trains  and click on them, double check which one it is against the sign on the platform, if there’s a delayed S-Bahn that is late I have to ensure I don’t go on that etc etc…. But it might be easier than it feels!

I'd add the stations on the rail planner before going to the station so it's just a click to get the next train. If it's one before or after the choosen one should be no problem. But as written before: I assume you'll see no control anyway. 

Thank you! Will try to do that I’ll be going the same stretch many times so might have to create a list of them...

I don’t worry about it too much. I try to get the correct one, but as long as the route is there I assume that’s good enough. It’s impossible with frequent S-Bahns
 

Unlikely to be checked, the inspector is unlikely to care, and if they care you can find the correct train if necessary and adjust it.

I agree with ralderton - for the likes of central corridor routes where you could be taking any of a number of trains in a 10 or 15 minute window then it is not worth worrying about at all.

The ticket inspectors will only be interested in whether you hold a ticket valid to get you from A-B on that day.  If you have activated a travel day then you are covered for that day.

In practice, I could put in an entry for the 14:32 S4 train, get to the platform and get on the S4 at 14:32, only to find it’s an earlier train that is running late.  Does this mean I’m on the wrong train - technically, yes.  Does this mean a ticket inspector is going to give a cr*p, absolutely not.  The other 99.9% of people on the train will just have a regular ticket which is valid on any train on that route and the ticket inspector is not going to sweat about that when they have a couple of hundred other tickets to check.

Long distance train, traveling a long distance - it’s more important to have the correct train details.

Long distance train passing through a central corridor in a city - in my experience these are never checked because they wait until the train has left the city and is on the next 20 or 30 or 40 minute segment before checking anything.