Is 4 full days in Split Croatia too much?

Hello! My girlfriend and I are booking an 8 day trip to Croatia in August, and we are trying to decide how we are going to split (pun intended) our time. Also good to note this is both of our first time traveling internationally.

We currently have a (refundable) hotel booked in Split for 5 nights (we arrive at 5pm to start our trip) and 4 full days. I was told by a colleague that this is way too much time in Split.

We were then planning on doing 2 full days in either Hvar or Bol and then 2 full days in Dubrovnik.

Does this sound like a good breakdown, or do people have better recommendations?

We are a young couple (both 23) and are looking to have a good balance of exploration, relaxation, and maybe a club or 2.