So did you see all the great villages to the east of salzburg or the nearby mountains just across the border in germany or the snow to the south within that one day on top of visitng the town? Train people should not be giving advice on how long to stay in towns as they have no idea about whether there are interestng things to do or see nearby. Salzburg is a 5 day minimum destination.Unless you are going to Salzburg for a particular reason 3 days seems excessive. It's kind of halfway between Vienna and Prague. I went to Salzburg as a stopover on the train between Vienna and Prague. Only really needed one day.
I was in Croatia in April. Split is ok but nowhere near as good as Dubrovnik. There are also a couple of national parks in Croatia, Plitvice and Krka, that I highly recommend.