Itinerary critique - Croatia 10 days

Hello! I wil be traveling to Croatia in mid September with my partner and would love some feedback and or suggestions. There are a few days I'm not quite sure what we could fill with, but overall we're looking for a more chill, meandering type of trip with a few scheduled things here and there. All our hotels are booked (Dubrovnik, Split and Zagreb) and we'll have a car. Thank you in advance!

  • Day 1 - Dubrovnik - 6PM arrival from west coast US, check-in and decompress
  • Day 2 - Dubrovnik - Explore Old town/spa day at hotel
  • Day 3 - Dubrovnik - Boat tour of the Elaphites
  • Day 4 - Dubrovnik - ???
  • Day 5 - Travel day - Stop in Omis or Makarska on the way to Split
  • Day 6- Split - Explore Old town
  • Day 7 - Split - ???
  • Day 8 - Split - Boat tour- Blue caves, and/or Hvar
  • Day 9 - Travel day - Stop at Plitvice or Samobor on the way to Zagreb, check in to hotel, nightlife Lower/Upper town
  • Day 10 - Zagreb - Explore, Dolac market or museums
  • Day 11 - Travel day - first flight back to US