I actually often edit a node four or five times after I press submit, for the first five to ten minutes. Sometimes it's in response to a CB that says I hosed a link or something. Other times it's just because I came up with a slightly different second take on something.
After I stop twiddling the node, I follow
the normal guidelines: no editing of the node, just adding
"<hr><b>update:</b> extra text" below if it's minor, or an entire new node if it's in reaction to a reaction.
If you're going to cache the "original" version of a node, I suggest a nominal cooling-off period of at least 15 minutes.
-- Randal L. Schwartz, Perl hacker