If you take a look at this particular revision history, I made an edit to my answer at
05:41:36Z, which is just under 3 minutes after the original timestamp of posting that answer at
05:38:43Z. This revision was noted despite my edit being made under 5 minutes. Normally a modification isn't recorded (or, at least, not shown) until an edit is made after 5 minutes has passed. This is the whole purpose of the grace period.
Has the system changed recently? If this change was indeed made, perhaps its intention is to encourage users like me to be more careful with typing up their original posts.