Yes. You could consider the direct Regiojet train and use those two 2 travel days for something else:

https://www.regiojet.com/croatia

Thank you!

So, every time you catch a night train, it counts as 2 travel days?

No, it counts as one day if you board a train and continue in that same train after midnight. But as soon as you change after midnight, it counts as 2 days, or you need a separate ticket.

https://www.interrail.eu/en/support/interested-in-interrailing/what-is-a-travel-day

@Maria Cruz  there is often a special offer of Croatian Rail (HZPP) with tickets just for 15€ from Split to Zagreb (Could only book these tickets personal in Croatia itself) so you could save one travelday of your pass Here a bit older tripreport :)

Here the Page of Croatian Rail found tickets from 100 Kuna  = 13€ (Just seats for coucheete or Sleeper you have to pay a bit more) for Split - Zagreb so why waste a travelday that worths 25-35€:)