We are traveling from Split to Dubrovnik spending 3 nights in Hvar and 2 in Korcula. Can we get ferry tickets the same day we walk on or should we get the day before or even sooner than that?
I don't think all carriers sell advance tickets, but outside of July and August it is doubtful you would need it. Note you can also travel between Korcula and Dubrovnik by bus. You cal always just walk by the kiosk at the waterfront and pick up a ticket the day before.
Krilo is the catamaran operator.
If you are travelling during the peak summer season, then you should buy your tickets online in advance, as this service does sell out. If you know your travel dates, book now. It’s a catamaran not a ferry. You don’t need tickets in advance for Croatian ferry services, as these take lots of pedestrians.
If you go on the Jadrolinija website and put in your dates like you want to buy tickets, it will show you how many seats are left on that catamaran.
We had no problem going from Split to Hvar to Korcula to Dubrovnik this past July on the Krilo fast cats (https://www.krilo.hr/en/). Buy your tickets in advance (a few days will work). They check tickets at the embarkment ramp where you get on the boat so you avoid having to look for the small shacks/ticket offices at the port (adds needless time and can be painful).