It would be great if we were able to choose (or there could be a default) how long posts could be edited for. Bettermode currently allows users to edit their posts at anytime, meaning you could post something that says something now and then in 5 weeks change what you said completely.
I've had active and potential users bring up the fact that having unlimited editing time on a post could lead to people saying one thing and then changing it up entirely at a later date by editing it, leading to miscommunication, irrelevant comments, or allowing people to say one thing and then change what they said at any time in the future to something negative or hate-filled.
Allowing each platform to set their own limits would be good, however, if it's easier/quicker/better to set an editing time limit for everyone, most social media platforms allow editing within 15, 30, or 60 minutes, so one of those options could be picked - 30 minutes seems completely reasonable to me, it's enough time to realize that your post had an error or you wanted to change something in it.
Users can always just delete a post and re-post it if they want to correct it or change what they said after that 30 minute window, or leave a comment to correct themselves or add additional content. I do see the value in unlimited editing times, but with the internet these days it's much better due to safety and communication reasons to set an editing window in my opinion.
Again, there could always be an option at some point for people to choose what they want as well, so if people do want it to be unlimited they can have that, or people can set a time limit.
Alternative solution - You could keep editing time limits unlimited, but show the history of a post, so show what it said before it was edited and keep a log that anyone can see of what the post was before it was edited and include a small icon to represent that it was edited on the post.
I would much prefer an editing window of 30 minutes though myself, and an icon to show a post is edited would be nice too. I'm not too concerned about having a log of post edits since it can make a post look a bit 'tacky' if it has loads of simple edits like grammar, etc.