Meta Ask HN: How frequently can I post comments?

I have increasingly been faced with the "You're submitting too fast. Please slow down. Thanks." message when trying to reply to comments.

I have gone as long as 3 hours between retries and still received this message. It may be longer still than that, and yet I see "conversation" style threads between people on HN, with as few as a few minutes between postings.

Any idea what is going on here?