We travelled this route in May 2014
Started at 11:00 am Zagreb, however the two lines out of Zagreb had been reduced to one due to instability of rail bed due to rains. The delay was two hours on the train in Zagreb. It then was a slow train to Budapest arriving about 18:00. Many stops in Hungary at every little station with a comedic check stop at the border.
The train eventually gets there but do not rely on efficiency and timeliness.
We were told our tickets were economy but we could sit anywhere, which we did with three other passengers. We move to an empty suite which looked exactly like the others, but were told it was second class. We purchased the tickets and invited a young Hungarian
gal who gave us some information and company. The conductor was interesting, he walked like a duck and would of made awesome cartoon character. No internet on this train, no food or drink. Wine cheese a book a nap and people experiences may make time go by.
Still a reasonable experience. about 4 years ago