Please mention your travel date.

Any day, even tomorrow, for example, if I change my mind about spending the night at the hotel and decide to take the night train to Vienna, can I do this a couple of hours before departure?

No, night trains have a limited capacity and they can sell out days or weeks in advance. A couchette cannot be sold twice!

I had a look and fortunately all coming days have availability: 35-50€ for a couchette. You shouldn’t count on space on the day though.

xD already im see price for ticket

Thank you, I’ll think about how to do it better, if I decide to leave and the places run out, I can go to Venice and from there also catch the night train, if there are places there of course

A sleeping cabin is 100 euros more expensive than a daybed, just because there are half as many people there?

It’s cheaper to buy 6 seats in a seated compartment and lie there

Just note that a reservation last only 15mins after depature from then it can be sold again from the trainstaff

To get the whole compartment you would need 6Tickets and reservations wich means besides your railpass you need 5 other tickets to book the whole seat compartment