As you may see: You plan to go to Wien on thursday and to Bratislava on friday = 2 days.
It's absolutely possible to do this with just one travel day if you start early.
I don’t understand.. why if i jump off to Wien at 07:58AM is just one travel day, but if i take just one another train of 1 hour, are two travel days?
It is simple
A travel day starts at midnight CET and ends at 2359 the same day. All trains you board scheduled to leave before 2359 that day are included until you get off that train. So boarding the Bratislava train is in the next travel day. That is why the experienced travellers above recommend starting early and making sure you maximise your travel days.
It also saves you any sleeper fares.
There is service from vicenza via Venice and wien at 9.03 that get to Bratislava before 7pm the same day.