Plane transfers

Theoretically.

But I would never take two unconnected flights where one is an expensive international flight.

I would go to Rome the night before. That is what we did when in the same situation coming back from Palermo.

Beth makes sense unless you can get one ticket. What happens if the first flight is delayed or even cancelled. The probability is low but it happens.

I'd do some research on ITA, although some use them routinely. Their on-time track record is borderline horrendous. They use Alitalia's old fleet and although their flights are cheap, unless you have time to burn and nothing in front re: international flights to the US, I'd find an alternative.

The ITA business model is to use the Rome airport as an hub, so Italian airports have an early flight to Rome, and around 9am there are flights back from Rome to all airports, so you can build any internal itinerary. The opposite happens in late evening. ITA has an incentive to run the early flights relatively in time or would have to reroute travellers. Traveling for business I have taken up to four ITA flights per day and time keeping was within reasonable limits. But of course you never know if there will be a problem on your specific day. If you are protected by a single ticket, and if the first flight is delayed you have to be rerouted, it is relatively safe. If you are on two different tickets you are taking a risk.

As others have said, ideally you want these flights linked/booked together so the airline has responsibility in the event of the first segment delay or cancellation. But if that option is no longer practical and your choice is to arrive at Rome a day early or take this flight with a 3 hour cushion, I personally would take the early morning flight. But if you are worrier or have a critical need to reduce risk, then reposition a day earlier.

Happy travels!

If you bought it as the single ticket trip that Delta sells, then you should be fine.
If something goes awry, its Delta's problem to fix.

I would not do it as a 2 ticket trip

I do like miuccia's idea to have dinner in Naples and train to Rome the night before and not have to get up at 330ish to get to NAP for a 635 departure.

I'd do some research on ITA, although some use them routinely. Their on-time track record is borderline horrendous. They use Alitalia's old fleet..

Re the "old fleet":

According to the airline’s statement, released on April 5, 2024, the new additions mean that 44 out of a fleet of 87 jets, accounting for over 50% of the fleet, now consist of new-generation aircraft. ITA explained that the fleet changes reduced the average age of the aircraft from 12.5 to 8.4 years in slightly over two years.

As for on-time performance, AZ 1268 NAP to FCO has an average delay of less than 10 minutes, per FlightAware. On an A320neo - which is new-generation, yes?

On my flight from LAX to FCO last November, on a new A350, I arrived almost an hour early; my friends, traveling on ITA from Miami, also arrived early. On my return flight connecting through Boston, we also arrived early.

I stand corrected. Goes to show that people and companies can change...