https://steemit.com/steem/@steemitblog/steem-version-0-12-0-released
"Preventing Edits after First Payout
To secure posts against defacement, it will not be possible to edit any post after the first payout. Future features via custom operations will allow authors to amend posts."
Hope this helps.
RE: No more edit option for my post (24 hours after publishing it)