Some folks say that after heat correcting a working part of the limb, it's a good idea to wait a week or more to allow some moisture to return, since the heat gun drives it out, sometimes to dangerously low levels. I've heard of a few instances of the limb breaking where the correction was made if flexed too soon.
I've never had a heat correction break, but don't build them in a hurry, so maybe they get to rehydrate afterwards by default.