Will only have one day in Rome and it will be on a Sunday so the Vatican museum and Sistine chapel will be closed. In the end of October how long will security lines be to enter St, Peter’s.
Hard to predict but we went on a Sunday afternoon and security line was minimal - maybe ten minutes. Also, there was a church service at 5pm on Sunday which was very memorable to attend church there even though I am not Catholic. Speech and singing alternated among several languages - English, Italian, Latin, and one or two others. Enjoy your trip!
I was there in December and January and from observation you need to Go at 7 am or 6pm to avoid the long line. But inside it should be less crowded on a Sunday since the entry via the Vatican Museum is closed. That is the way we entered St. Peter as part of a tour group.
End of October should have shorter lines than other times of the year. No way to know for sure, though.
We were there late October and each line had 10-15 people on it. Did not take too long toget through.