I feel that 5 minutes was reasonable given it wouldn’t be seen by too many people yet.
I am extremely used to typing my comment out and then noticing my many grammar mistakes afterwards.
It’s often that it takes me multiple attempts to fix my comments, especially given how bad Google Keyboard has gotten with autocorrect.
kinda agree here, but I will say, typos and transpositions excluded, it does make me consider my initial comment a little more carefully - so perhaps a perceptible improvement in overall interaction? I do agree with other comments that it should probably be an instance choice (range hard-coded) as to when something is marked as edited.