The huge majority of forums (in the high 90% range) have a time limit on when you can go back and edit your post. The default limit is typically 15 minutes.

It keeps people from saying something that goes against whatever TOS is in place and then deleting it when confronted.

Personally I think unlimited is going to end up causing some problems. Won't know until it happens.

1 day is more than reasonable, and if you want to have something edited after that, contact the forum mods or KD or DocJohn.