« first day (21 days earlier)      last day (32 days later) » 

8:48 PM
I'm recycling this room for another topic: Windows NTP Precision
1. documented precision of Win7 Time Service: a few seconds (worse than 1 second).
2. ping compensation of NTP & Windows Time Service: certainly yes, already exist.
3. alternative NTP softwares: #to be answered by others#
Since I've answered 2 out of 3 of the concerns of your question, I'd prefer you update your question to narrow/restrict the scope of it, so that the bounty would really help solve your problem but not attract easily research-able stuff (which i already have done).
In particular I want answerers with actual experience in the 3rd party NTP softwares they recommend. Do you agree with that? Please also state your request to be included in the bounty notice.
 
9:27 PM
Reference on 3rd party publishers of time and frequency software & hardware for extreme high accuracy needs
 
 
2 hours later…
11:18 PM
keywords: delay, offset, jitter/dispersion, correctness interval,
synchronization distance/root distance = delay/2 + dispersion
 

« first day (21 days earlier)      last day (32 days later) »