It's very intensionally all over the map---UAL has been candid that they are looking for a diverse group of candidates to interview as long as the minimums are met.

That said, those on the lower end of the experience/flight time spectrum that receive the call have something else in their application to get UAL's attention (letters, references, academic scholarship, awards, prior UAL/CAL internship, etc.) compared to others with similar experience/flight times.

There is no single magic bullet but there are plenty of combinations of bullets.