I have a sort of “staircase wit” ( I realise what I should have said when I leave the meeting and walk down the stairs). As a result I edit my posts quite a lot.
Is there any guidance about best practice on this?
At the moment I am considering posts fair game to edit if no-one has replied.
I know people can see the history of what I write, so there is a trail to unravel in a dire case of miscommunication.
I’d say edit all you like and have some fun doing it 
As long as the meaning is not changed then editing your posts is fine.
Checking for replies is also a considerate thing to do — if there are no replies, then you are free to edit as much as you like.
Until the post edit time limit kicks in it seems (as I just found out when I tried to edit my original post 
) and searched for why I could not.
Yeah, that’s the approximate guideline I like to follow. Sometimes my edits do change the meaning of the post, though, because of stuff like a word being while writing the post.
I would recommend that users follow the conventions of each specific forum.
For example, several that I’ve participated in use “ETA:…” or “edited:…” on a reply to indicate additions or alterations, typically in an effort at transparency (as edits are hidden from most users).
One group in the past tended to italicize edits that weren’t mere typos or autocorrect fails.
Another group didn’t seem to care.
My thought about how long is reasonable after posting is that just because no one has replied does not indicate that no one has read the post, so keeping edits as transparent as possible is simply courteous.
In general, if you still have time to edit, go for it! 
