Lines at security at FCO
can be long, depending on which terminal you use.
Remember that concourses are connected airside, so you can clear security in the terminal AZ
is using (forgot the number) and then walk to the other concourse.
Between 90 and 120 minutes should do the job. If you need to check in luggage at a counter, add some extra time.
With only hand luggage and OLCI performed, 75 minutes or slightly less can do.
Keep in mind that there is some walking involved if you arrive by train.
Not sure if past-Xmas is particularly busy at FCO
Any chance you are flying KU
? If so, extra time is required, as AFAIK it is using non-Schengen gates.
Carpe diem ! Life is too short to waste your time ! Keep in mind, that today is the first day of the rest of your life !