Okay, we just did this in the past week. I think the T1 test site is in T1, before security, but we made appointments for this past Monday (we flew out Tuesday) at the T2 Randox (as we, and your, will be flying from T2). It is walked to easily from the bus drop-off point in front of T2 -go inside T2 and immediately go up a level, take the bridge back across departure road, come down, and then follow the signs. Note this does not involve checking-in or going through security. As we were staying these 2 nights at a hotel near the airport, we had free shuttle service back and forth. They are efficient at Randox, there was a walk-up line, and appointments skipped it. We went back after the test to sit in T2 to wait for our emails (iPads, not phones). If this is timed within 24 hours of your flight, you may be able to complete check-in at the counter before leaving. I do not know about other airlines, but we were using American and were able to upload the results via the Verifly app and were able to then do an online check-in and get our boarding passes, counter not needed. Note that if you are downtown and need to take the bus (41, 42c, 33, 16) to the airport, it is 3.15 Euro a piece, cash only, exact charge only, each way. BTW, for tests on April 25, we made the appointments on the 23rd, and probably would ahve been fine doing this on the 24th.
Also note for your flight day, Dublin Airport has still not fully recovered staff-wise, and it will take you longer to get through. The general security line was only about 20 minutes, but the processing of all going through pre-clearance was very slow. Well over an additional hour to clear this, even though the TSA security was bag check only, and immigration only looked at our passport against a picture that they took. Plan this for the day before, even if it means the expense and time of the bus from downtown.