How long to clear customs FCO Rome

You will need to clear immigration. It didn’t take us very long in Rome.
Customs is for duty on goods you might be bringing back to the US.

Customs doesn’t take more than a minute
Passport control/Immigration can take time depending on how many other flights landing
It is all automated now

Will this be your first entry to Schengen?
Will you have checked bags?

You don’t usually have to worry about giving an accurate pick up time- just provide them with your flight number
Any good limo service will monitor your flight

Or simply take a taxi -fixed rate 55 euros, no tip

It's generally faster now at FCO, even for non EU citizens, as it all done by face recognition technology, passport scanning, and AI. You won't even need to talk to a human immigration officer anymore. But of course it will depend on how many international flights arrive simultaneously.

If you book a private limo service, they will wait for you at the arrival hall with a placard with your name after baggage claim and they know when they show up based on the flight information you give them.

If you prefer a regular taxi (55 euro flat rate, all inclusive), just walk outside to the taxi stand. There might be a line of people, but there are dozens of taxicabs lined up, so it generally goes pretty fast.