how much time is needed changing planes in Newark

Can't tell without knowing whether this involves changing terminals. Which airline(s), from where to where? For me, flying from the west coast, that would be too little margin in case of a delayed first flight, even within the same terminal. But I'm more cautious than some others.

If you're doing the whole thing on one ticket, the airline will get you to Shannon on a later flight if necessary. Otherwise you're taking a big risk, I think.

If you can check your bags through to Shannon , your in the same terminal and your flight is on time then yes. If you can't check your bags through to Shannon , then you maybe cutting it close. Newark airport is small but finding your way to the monorail if you need to change terminals is cumbersome , you also need to factor in ,flights aren't usually on time.

Annual flights stats for 2022 records 67.6% flights on time for Newark. Are you comfortable with 1/3 of the flights being delayed?

Annual flights stats for 2022 records 67.6% flights on time for
Newark. Are you comfortable with 1/3 of the flights being delayed?

That would work in the OP's favor as it would give them more time to make the connecting flight.

Thanks everyone, It is a United flight but I'm not certain which terminal we arrive and depart from. We will be arriving from Nashville to Newark.

Given UAL is selling it as a single ticket means it can, and at least almost always is, being done. Otherwise they would have an expensive ongoing problem of getting people on other flights.

I have done that connection, but it was too stressful for me and I won't do it again.

As I live in NJ, I fly out of Newark all the time. FYI, there are 3 terminals A,B,C and were connected via the monorail. However, the monorail was not extended to the new Terminal A, as the monorail is to be replaced. If you are flying into A and need to change terminals, you will be have to take a shuttle bus to Terminal B and if need be, take the monorail to Terminal C station.
Important to build in extra time if you are changing terminals. Your time frame could be problematic if plane is late and I don't know frequency of terminal A shuttle bus runs. And it is not a hop skip and jump from monorail stations to gates.

Both flights will be in C terminal. C terminal however has three prongs and the worst case walk between C gates is not short. If you're lucky, same prong and short walk.

Your choice is 5 1/2 layover or a 1 hour 11 minute layover. Personally I'd do the 1 hour layover but if you're worried about it pick the earlier united flight.

I have taken the Shannon flight out of Newark on United--Boeing 757. No issues.

Happy travels! Ireland is lovely!