Thanks for the motivation and detailed explanation of your users’ behaviour and beliefs. Always good to get experimental evidence, as it were.
I have two immediate reactions: one is for the mechanism to separate edit and posting actions, and allow (for example) one of each. And the other is that 24 hours is a very slow slow mode: did you try say 1 hour and find it not slow enough?
Another thing to add, as an anecdote: on another forum I use there was the possibility of setting it to show or not show people’s edit counts on posts, and in the discussion about whether to enable or disable this facility, it transpired that there was a set of users who very much did edit their posts, several times, as they discovered things they had not expressed well or not typed correctly. (These people felt that showing edit counts was shaming them, whereas the idea was, I think, to advertise and discourage after-the-fact substantive changes to posts.)
Although that forum did have a preview facility, some fraction of users did a lot of editing after submit. In this case, a slow mode for edits would be unwelcome to those users, and perhaps have a chilling effect such that they felt shut out. (Personally I favour the idea of a time-limited edit window, of say 15 minutes, which allows people to express themselves as they like, but doesn’t allow them to change what they’ve said at a much later point.)