I have reviewed this document as part of the Operational directorate's ongoing effort to review all IETF documents being processed by the IESG.  These comments were written with the intent of improving the operational aspects of the IETF drafts. Comments that are not addressed in last call may be included in AD reviews during the IESG review.  Document editors and WG chairs should treat these comments just like any other last call comments.

This document is well written, and is ready for publication.
Only a couple of nits, for the authors consideration:
1. In the abstraction and introduction, you state "Since it does not affect the wire protocol, the Khronos mechanism is applicable to any current or future time protocol." I do not think "any" make sense here. This document only applies Khronos to NTPv4. You may say, it "could be applied to other time protocol".
2. Khronos is a technique firstly described in one paper. I would like to see the reference at the first place, e.g., in the introduction.

Best,
Tianran