By rules - the delivery is made to the consulate of Italy. For filing through the consulate (visa center) of Poland, you need to add accommodation in Poland on the way there or back. Theoretically, it can then be canceled.

The visa needs to be requested for a transit two-time visa. Justification of the required number of days in the Schengen stay (in your case, optimally 9-10) - confirmation of booking of transit hotels and description of the trip plan.

There are many additional nuances that are difficult to foresee ...

Do you want a reliable positive result - book hotel reservation in Poland to an accredited operator and ask him to arrange the required visa. It will surely be somewhat more expensive than the usual procedure, but without the need for several personal trips to the visa center.

By rules the visa opens the country of the first entry. It is necessary to apply for the Polish Schengen multivisa, attaching also the confirmation of the armor to Croatia. Croatia in Schengen does not enter yet, you need to get a separate visa (in the summer in Croatia, visa-free entry, if not canceled).

P.S. Perhaps the Poles will redirect you to the Italian consulate, because there you have a stay for 1 day more (as lucky).

Up to 30 June in Croatia you can enter the current Schengen multivisa or the national Croatian visa. From July 1, the entry rules for Schengen visas can be canceled, but this information will be known later.

This is a question for the visa center of Italy, Poland and Croatia . Croatia this year makes entry for visas.