It has more to do with how they do shit than the fact they offered breakfast all day.
None of their competitors have issues serving everything on their menu at any time they are open, but none of those other restaurants are that picky about burgers, sausage patties and eggs being cooked on the same griddle.
The craziest time of day at the McDonald's locations I work at is the switch from breakfast to lunch, because they have to practically transform the kitchen. It's ridiculous.