Well Zapdos and Moltres took about 2 hours each. But copared to Latios that is nothing. Encountering was easy, but I ran him to minimum HP and to the point where he had to use struggle about 5 or 6 times and still couldnt catch him with 70 ultraballs and 10 timerballs.
Articuno was the one I HATED because I would always go in the wrong entrance to Sea Foam Islands, there were always a million wild pokemon, and I almost never bought enough ultra balls so I would have to restart and buy more & do it all over again. Not to mention every time it used ice beam I would get frozen