Hi, no if you have to change train than you will use a second travel day.

But in this case the thing is a bit complicated. Because half of the train continues to Zürich and half of the train stops at Basel.

In your case, does the train not travel to Zürich or is the part to Zürich full? Because you could add as your train in the Railplanner app till Zurich and change in Basel to the seat carriages of the same train that travel to Zürich.

I’m taking the OBB nightjet to Basel because the direct sleepers to Zurich are sold out. If I didn’t have eurrail pass I’d have to get a separate ticket from Basel to Zurich. So do I have to use one or 2 travel days?

Also, I’m not sure I understand the time window that makes up a travel day. Could you please explain? Isn’t a night train an exception to the typical time window?

The app does not know what reservation you have and you could add to the railplanner app to get your ticket the train IC or NJ Amsterdam to Zürich and use your reservation for the part till Basel. 

Technicly there are on this train 4 trains. the seat carriages run as Intercity one half till Basel, the other to Zürich and the Nightjet (sleeper and couchette) the same two trains one half to Basel and one to Zürich. But often the app has no data for the Nightjet and you find only the Intercity. I'm not sure if it would be fine.

Maybe @rvdborgt or @AnnaB knows more?

Time window is 00:00 CET to 23:59 CET. In this time you can use so many trains you can. If you enter a train before midnight, or to be correct the sceduled departure time of the train (has not to be a nighttrain) is before midnight and you arrive after midnight (without train changes), it will count only the departure day. If you change trains you will need a new day.