During busy times, we've waited as early as 20 minutes before... we've done this twice, both during busy times. The first time, my girls were first... the second time it was just my son and although we were first waiting, we didn't get "picked" for a creation until around 6 other kids had gone. So it really doesn't matter if you are first "in line" it's whoever she picks.
This one guy who was standing with his son almost behind her on the side really got upset because when I was standing there he came up and asked how the line went, I told him there really wasn't a line and he says well you are first, they (another group) are second and we are third. Well after the 4th or 5th kid had gone, he started yelling "hey there is a line here, WTH" basically to me and I tell him the same thing I told him when he first approached me, she chooses, there isn't a line. Miyuki tells him the same thing, smiles at me and tells me my son is next... LoL. I don't think the guy ever got one for his kid.