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.
Can’t comment on 5min cooldown - it never mattered to me.
In regards to keyboard - I’d suggest switching to Florisboard. It has no autocorrect, which I missed a lot at first, but now that I’m used to it - I love it.
It’s also very quick compared to swiftkey, which uses to be my poison.