Croatia

One full day in Split should be enough. Make sure you check ferry sleds closely. There are regular ferries from Split to Hvar but I don't think there are any direct Hvar to Dubrovnik ferries especially in April. You may want to visit Hvar from Split and then take a bus to Dubrovnik. They run frequently and take about 4 hours.

We were in Split as a stop on a cruise in October 2011. (The upside of a cruise is you can get to hard to get places easily, the downside is no chance to linger). I think Split is easily worth two nights and one full day. It really is the kind of place where you might want to slow down and just be there. No overwhelming sights, just a very pleasant town. Weather for us was fantastic; I rely on Yahoo weather for travel planning. Give it a try, it's great!

One full day is adequate to see the main sights in Split. April is low-season for ferries, so your choices are more limited than if you were traveling in high-season (June-September). Based on the Jadrolinija schedule, it appears the coastal ferry from Split to Dubrovnik won't run in 2013. You might consider staying an extra night in Split, day tripping to Hvar and then taking a bus from Split to Dubrovnik. An off-season day trip will likely require taking the early 2 hour car ferry to Stari Grad (Hvar), bus to Hvar town and returning on the late afternoon car ferry, turning 2 hours of high-season catamaran travel into about 5 hours of ferry and bus travel. Stop at the Jadrolinija kiosk near Split harbor to confirm your options, as schedules can change. Another option is to take the afternoon Krilo catamaran to Korcula town for an overnight stay and then take the bus to Dubrovnik. Avoid the Jadrolinija catamaran that only stops at the opposite end of Korcula island. There are small boats and some ferries from Dubrovnik to the nearby islands. For Jadrolinija ferry details, check low-season tabular schedules on their website – Split District for Hvar and Dubrovnik District for nearby islands like Lopud. For the small boats, it might be easiest to just check their schedules once in Dubrovnik.

Half a day in Split was enough for us. We were ready to move on, and enjoyed other places more.

Other than the area around Diocletian's Palace, Split is a modern busy city. A half day for the Palace was plenty for me. Near by is Trogir, the ancient city island town connected to the mainland by bridge. I'd suggest spending some time there. Ancient architecture and great food with a quieter atmosphere.

Take some time to hike up Marjan Hill in Split - it's gorgeous, woody and has fantastic view of the city from the top (as well as some old Croatian churches). I bet most toursits don't make it there. The hike can take a few hours, so there is definitely enough to do in Split for at least a day. Trogir is also highly recommended and close.