Generally, they surface right away; look at it like this, if it fails, your classic forum is still there, so you won't have a non-working forum.
You could have someone (:ahem:) redo your style for you, numerous people (:ahem:) do style work rather cheap ($30/hr) for ubb.threads.
I've moved over a few classic boards; they take the longest to move over, but you'll definately appreciate how much faster threads is compared.
