I’m kind of surprised this one hasn’t come up in any of my searches.
When I look at the origin on several sites it says:
I heard somewhere that this phrase actually comes from the French “à toute à l’heure”.
Doesn’t this seem more probable as horribly mangled French than some strange form of “toot”? I guess I’m wondering if anyone knows why the mangled French theory of this origin seems to be discounted.