Many forums handle this with an iron fist, limiting "edit" time to 15 minutes... How much better if the message could simply be "saved for later...?"
Minor problem with this suggestion: if people are unable to post messages immediately, they may post fewer messages. Less forum activity is not good for small forums.
Solution: a "delay" setting which will post the message automatically after x minutes or x hours. This might be simply a modified version of the standard "moderation" settings where all messages require moderator approval--except for any message to be "approved" automatically--AND editable.
1. Slightly modify the existing "moderation" options. Have an "auto-approval" setting which will automatically "approve" the message for posting after 1-96 hours--AND enable the person posting the message to VIEW AND EDIT in the meantime.
2. "[Membername] is posting a reply." An immediate message displays and reserves the space for a reply, as if the reply had been posted immediately. I.e., the reply is already there, but only the posting member and a moderator can view and edit it, until the wait period is over. This wait period to be set by the administrator for 15 minutes to 3 days, as desired. Therefore the member posting the message need not be anxious about "losing his place" in the thread--and the other members can be assured that a reply is forthcoming.
3. "Think it Over" button. In addition to the "post reply now" button, a "save for later" or "think it over" button. This saves the message indefinately. Also, each time the member logs-in, a pop-up alert reminds him of his "save-for-later" messages. (Next suggestion below.)
4. "Your pending replies" pop-up alert. This can be added to the same alert for "conversations." This can be used both with the 'auto-moderation' option 1 aboe (which automatically posts replies after x hours). And also with the 'think it over' option 3 above (which saves the reply indefinately until the member decides to post it).