(I've already posted about this in a response to a post in which the subject came up, but I figure it's probably a good idea to post it here too to make doubly sure people get the chance to read it.)
The allowed time limit for modifying posts has changed. Previously it had been 90 seconds, but now it's 2 minutes. 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.
