We flew out of FCO to IAD on Jan 3, 2025. Notes:
- We caught the Leonardo express at 6:50AM for a 9:55AM flight departure. Train was not full; there were open seats on the train. Train arrives essentially at T3, but I'd estimate a 10min walk to your check-in area
- For the Leonardo express, I bought tickets ahead of time online. We arrived at Rome Termini much sooner than expected, and I was able to easily change our departure time on the Trenitalia app. No extra charge. If you buy through the app, then the ticket automatically validates at departure time. If you buy a ticket in the train station, then you need to manually validate the ticket. I don't know how that is done, but the conductor did check everyone's ticket. If you have not validated, then there may be a fine (50euro?).
- We flew United and so the online check-in allowed for entering passport and checked-in bags. At the United counter, we did the self-serve kiosk for tagging our bags.
- Security had minimal waiting time.
- We were at our gate by 8:30AM at latest.
Everything ran efficiently, no complaints. Not sure how this would have been at other times or other dates, but this was our experience.