Seems a reasonable connection to me.

You’ve clearly got a plan for what to do if you miss it, which is the most important thing.

i would book the connection, with the same backup plan a as you. 

Croatian railways will then have to find accommodation for you. Not sure how that works in practice though.

It's no ÖBB train, it's one from Slovakia (ZSSK), that is not cut down to Wednesdays only, it has just no confirmed timetable for the departure dates for June 7th and June 9th departures - that's why it's not shown for that date.

Interesting answers from all, many thanks.

Rvdborgt: I would love it if Croatian railways were prepared to put us up for the night - but as you say, one can only wonder how that might work! Do they take responsibility for the IC 204 from Budapest to Zagreb arriving on time? Wouldn’t they just say we should have arrived by the morning train instead? There’s one sure way to find out… !

Hektor: You’re right. ZSSK themselves sent me the timetable (with a link to ÖBB for reservations) and it was there sure enough (for June 7th)… and then the next day it wasn’t. Which makes me more than a bit cagey, as our IR trip starts with Paris-Berlin on ÖBB’s NightJet on Thursday 16th May —all booked up— but now (i read in the press) that train only departs on Saturdays, instead of 3 times a week. And sure enough, it’s no longer listed. I contacted ÖBB 3 days ago. Still no reply. But as you say, the NT 1821 is a Slovak train, so whether ÖBB lists it or not shouldn’t have any bearing.

I miss the big red Thomas Cook Railway Timetable of Europe of 30 years ago, and just playing it all by ear from one stop to the next. Thirty years down the track and a wife in tow, things are so much more complicated…

Update (@Hektor in particular): ZSSK have stopped displaying the NT1821 on their own site now except on Wednesdays… so something’s up. This runs contrary to what they told me themselves in a very kind email they sent just 4 days ago. It was listed for Friday June 7th four days ago and now it isn’t. Pfff.

edit : not NT 1821 from Bratislava to Split (via Cilje) but EN 1153

Epiiogue

We’re back, after a great trip around Central Europe.

For anyone who might pick up on this thread, here are some “key learnings”…

1. The ZugFinder statistics were misleading. ZugFinder passes on whatever data it is given by operators, but doesn’t collect feedback on that data from users. The Budapest to Zagreb train is, from what we heard on the ground, usually late.
2. We had 31 minutes to make the connection in Zagreb. By the time we joined the Budapest to Zagreb train at Balatonszentgyörgy it was already 19 mins late. At each station, it picked up another minute’s delay. No problem, i thought, as the train had a couple of scheduled long stops (20 minutes or so, inside Hungary and at the border) giving them enough of a margin to make up some time… instead of which, each 20-minute stop lasted at least 25 minutes.
3. Croatian Railways took over at the border. New locomotive, new team, and, by sharp contrast, were determined to make good time. They checked with all passengers to see where people were getting off, and even skipped two stations, going past slowly, i suppose just in case anyone wanted to board. Otherwise the train went like a bat out of hell…
4. But it still reached Zagreb 45 mins late.
5. The happy end: the Zagreb to Split night train had been deliberately held back, and was waiting for us on the other side of the platform! I don’t know whether they always do that, or just arranged it on this occasion because there were about 40 Interrailers on the train (and it can probably be assumed that most were aiming for the night train).
6. Bravo Croatian Railways. It would have been nice, however, to have been given the good news a little earlier, and not while we were standing at the train door with our bags, ready to leap off, and with blood pressure running high.