We realize that most posters were probably glad that the time limit on edits works very differently as of the most recent upgrade, but 1) I can't guarantee that the SMF creators won't bring it back as an actual limit with the next version
Tonight I installed a mini-upgrade, and it's actually back already. However, it's slightly different that it was before because now there's a 2 minute time limit (it had been 90 seconds). That's until 2 minutes after the initial posting time or the last time the post was modified. But one thing you have to keep in mind is that the system extends you a courtesy of 90 seconds before it will log the modified time (that's so that if we have the "Show time of last edit" feature turned on (which we don't at the moment), and if you modify anything before those 90 seconds expire, the edit time of your modifications won't show up at the bottom of your post).
Trust me, it sounds more complicated than it is. A good rule of thumb would be to start making any modifications to your post before 2 minutes expires. Or better still, try to catch anything that you might want to change by previewing what you've written before posting it.