It really depends on the amount of games people have and the way emulationstation caches and loads everything the first time it boots. For large amounts of games, it can take 30-40 seconds, maybe more, for a decent amount, perhaps 20-30. You could always go with a happy medium of 20-30. Personally I don’t care too much as I typically leave my pi on, so its rare I boot it up. But when I do, I don’t mind admiring my boot video while it boots.