I think you have too many destinations for what appears to be a 9-night trip. You have part of a jet-lagged and possibly sleep-deprived day in Zagreb, during which it would be best for you to walk around outside (the historic center is very nice). There seems to be no time for any of Zagreb's many museums.
You'll have just 1-1/2 days in Rovinj, and you'll find getting around Istria by bus rather slow going. I usually recommend 4 nights in Istria even if people have cars.
Traveling from Rovinj to Plitvice will require a connection (probably best in Karlovac, but I don't know how many buses go through there every day) and will not be a short trip. You probably won't be able to get to Plitvice before mid- to late afternoon, giving you time to see no more than part of the park that day (assuming the day-trip crowds have dispersed by then). You'll need some early-morning time in the park the next day, meaning a not-early start for the next leg of your trip.
I think traveling by bus from Plitvice to Ljubljana means going back through Zagreb, not a short trip. With the late start and the long trip to Ljubljana, I anticipate a rather late arrival there and only one day in that city.
I think it's possible you would do better to route yourself Zagreb-Plitvice-Zagreb-Rovinj-Ljubljana-Venice. As of 2015 tnere was at least one morning bus from Ljubljana to Rovinj, so I assume there's a bus running in the opposite direction these days--though I only found a late-afternoon departure after some quick research.
It's harder to get hold of reliable online bus schedules than train schedules, and you have absolutely no slack in this itinerary to deal with non-existent buses. There's also the issue of often-thin or non-existent bus schedules on Sundays (and holidays, if any). I really think you need to drop a destination.