Times for Dublin Pre-Clearance

I'd say you are cutting it pretty close. My experience was during the summer which may be busier but you essentially have to wait in line to check in, then you have to go through airport security (another line), then you have to go through customs (third line). Allowing three hours would not be unreasonable.

If you are interested, you can monitor historic preclearance queue times by checking the US Customs website:
http://pqt.cbp.gov/

Example report for March 8-14:
http://pqt.cbp.gov/report/DUB/03-08-2016
Looks like peak queue is in the 9:30 to 10:30 time frame with 10:00 being the worst (3-10-2016 at 10:00: 27 minute queue). Must be caused by all these passengers heading for Philly arriving 2 hour to 90 minutes before the 10:20 am flight. On 3-08-2016 the wait peaked at 10:00 am and was only 10 minutes.

Edgar, I would really love to look at those, I had found those links earlier. but they won't load, neither on Firefox nor Safari. And neither if I click them from here, or find them directly on Google.In fact, no CBP sites are working!
Any suggestions?

Try a search for "us customs preclearance queue" or "us customs and border protection preclearance queue times". I'm using Chrome Google search.

I came back through Dublin last May and I would recommend arriving at least 3 hours before your flight! We were planning on arriving 2 hours early but the desk at our hotel warned us that we wouldn't have enough time and they were correct. The lines move slowly and you have lines for check-in, security, US customs, and another for security at the international gates. You can always get up a little earlier and have breakfast earlier!

I would also recommend getting to the Dublin Airport at least 3 hours early like others have mentioned.