Two nights can work if the trip is coast-first and simple
Split is easy enough to enjoy quickly if the plan is compact and the hotel is well positioned. Two nights can already cover the waterfront, the historic core, and the general mood of the city. That version of Split usually works best when the city is one stop on a wider Croatia route rather than the entire focus of the trip.
It is enough for a strong impression, but not for much slack.
Three nights is the strongest first-time answer
For most travelers, three nights is where Split feels right. You have enough time to settle into the city without turning it into a slow stay that overstretches the experience. The extra night helps because Split is partly about how the place feels when you are not pushing the itinerary too hard.
Three nights is also the cleaner answer if you want the old town, food, and some relaxed waterfront time in the same trip.
Four nights depends on whether Split is the base or the goal
A fourth night makes more sense when Split is functioning as a base for a slower route or a broader Croatia trip. If your interest is mainly the city itself, many travelers find that three nights is enough. If your interest is a slightly more relaxed coastal rhythm, four can still work.
The question is less about what is possible and more about what kind of trip you want Split to be.
Location and season shape the answer
In Split, hotel area and season affect trip length more than people expect. A central stay in a comfortable month makes the city feel easier and more complete even over a shorter window. A weaker location or busier period can make the same number of nights feel less efficient. That is why the smartest answer usually combines length, base, and timing together.