In an effort to meet departure times, some airlines (worldwide) seem to have adopted an earlier than printed (on the boarding pass) boarding start process. This doesn’t seem to be happening at every airport with every airline but I have been hearing about this more and more from readers, airline employees and frequent flyer contacts.
This means that if you aren’t there a bit early, you may not board the plane early enough to get space in the coveted overhead bin. This is even more problematic for frequent flyers with special boarding privileges that may not be aware and get stuck having to gate check their carry-on bags.
The moral or the story is to show up to your gate at least 20 minutes before the printed boarding time on your boarding pass.