US Preclearance at Dublin Airport can take anywhere from 5 minutes to 2 hours. But in most cases, you are looking at a 20-40 minutes wait time.
Also, remember before you get processed there is another security check, this, however, moves relatively quickly (remove shoes, jacket, electronics from your bag, and liquids) the majority of your wait time is actually for visa/passport checks with an Officer.
|Traveler Type||Average Wait Time|
|Irish/European Travelers with visa/ESTA||20-40 minutes|
|US Citizens||15-30 minutes|
|Permanent US Resident cardholders||20-40 minutes|
|Global Entry Members||5-10 minutes|
Always give yourself enough time, it is better to have extra time as you never know what delays might present.