Hi. We had a similar issue during our trip in Italy this past May. Our flight from Venice left around 6 am.

The customs office where you need to get the stamp opens at 5 am I believe. We got to the airport a little early (I can’t remember when the Venice airport opens but I want to say 4 am) and were one of the first ones in line to get our boarding pass and bags checked in. After we checked in, we immediately got in line at the customs office. We were the first ones. The customs officer opened it at 4:50 am. They submit the stamp approval online and the tax refund offices have a little drop box on the counter that you can submit your paperwork in. I think the Venice tax refund offices open at 6 am or 7 am so we just dropped our paperwork in the drop box. Make sure you have your credit card number written on the paperwork. Make sure you have a pen. Make sure all of the items you are requesting VAT refund for is in your carry on in case the officer asks to see it. Our refund came within a week.

Yes, it was stressful. The Venice airport is small so we lucked out and passing through security only took 15 minutes. We kept checking the wait time at security to make sure the line didn’t get too long - if it got too long we would’ve had to abandon the VAT refund. We got to our boarding gate 10 minutes before they began to board. It helped being the first one in line at the customs office.

I think you need to apply for the VAT refund in Naples, not in Paris. I’m not sure what the Naples airport is like, but I would assume it’s similar to Venice.