How long does US Immigration/Customs take in Dublin?

We went through the U.S. preclearance and customs and I think it took about an hour - there was a line. But of course time could vary. Here is a link to where you can download the customs form to complete ahead of time. It also explains the preclearance process.

https://www.dublinairport.com/at-the-airport/passenger-Information/us-preclearance-facility

We did this in April for a flight leaving Dublin at 11:20 on a Tuesday. We were concerned having read of the large number of people due through around that time. There was no issue whatsoever, our time in pre-clearance was just as quick or quicker than what we get at our home airport, Philadelphia. They have the kiosks, which move things along. I would say there was more time spent answering annoying questions from someone at the main desk area as we were not allowed to do online check-in. Really, answering "retired" as to what we do was not good enough, this person had to know what we did before we retired before she'd let us go on?

In any event, we arrived with close to the 3 hours advance, and even with having to check-in, 2 security checks (there's a second one for US planes) and pre-clearance and found ourselves with 2 hours to ill in a terminal with little going on.

We got to Dublin airport for our return trip to the US two hours before the flight, and that was plenty of time. I know that the airport advises three hours prior, but my suspicion is that they want you to spend an extra hour in their duty-free shops.

We did this last June, flying from Paris to Dublin to Chicago. I'd guess it took well less than 30 minutes to get through. And when we arrived in Chicago, we were able to just leave the airport immediately.

If both flights are with Aerlingus you will have no problem. We had a similar situation, about 1.5 hrs between flights. Our originating flight left late so we had even less time. Aerlingus is very organized. When we were going through US customs we voiced our concern and they told us our situation was common. The Airlingus personnel assured us we would make our plane. They actually held the plane for us and we were the last to board, but we made it! Similar situation encountered in May when we were in line at US passport control and there was a family worried they would miss their connecting flight. Aerlingus personnel went to each line and asked if there was anyone on certain flights. If so, they were moved to the front of the line. Must say Aerlingus is very well organized and make sure you are taken care of.

Thanks to all, your advice has been really helpful. I feel much more comfortable now about my connection to LAX.

We did this two days ago, and it was very quick and efficient, with barely a line. Several things to keep in mind is that once you go through US Pre-clearance, there aren't any real restaurants or shops. We only found a coffee shop (although I didn't go all the way to the end of the terminal). Also, keep in mind there are two security checks, with different rules. One needed shoes off, one didn't. One needed liquids in clear plastic bag, one didn't. They both needed my iPad removed from my carryon bag, which never happens to me in the US.