When I checked with Hyannis after I went over 6000 miles, the longest they quoted for, if I remember correctly, was 5 years. When I checked at 4700, they offered a plan up to 8 years. You can see what plans are available here:
https://hyannishondacare.com/questionnaire.php
Here is what another online dealer Sarcucci Honda said, which kind of explains the difference:
All "C" and "D" plans start at the original in-service date, and 0 miles(Vehicles under 6,000 miles).
All "F" and "G" plans start at contract purchase date(Vehicles over 6,000 miles). Seems like once you are over 6000 miles, you might as well wait until near the end of the regular warranty period.
If I remember correctly Sarcucci were a little more expensive, but their site is more informative. They have a copy of the contract.
https://www.saccuccihondacare.com/coverage.php
I got some "what-if" quotes from Hyannis and unless I am misreading the quotes it appears to be counterproductive to not wait until near the end of the regular warranty, and you could even end up with a shorter warranty depending on when you purchase it.
First quote was for purchasing at 2,000 miles which is about where I am at now:
Code - Years - Mileage - Rate
D82 - 8 - 120,000 - $1,564.00
* Coverage for a New Honda vehicle begins when the vehicle is originally put into service at zero miles.
So this would be coverage for years 4-8, at $312 per year (1,564/5)
Second quote is for purchasing at 7,000 miles which I estimate I will be at around December:
Code - Years - Mileage - Rate
F52 - 5 - 120,000 - $1,319.00
* Coverage for a Near New Honda vehicle begins on date of plan purhcase [sic] and expires at the end of plan terms or stated mileage, whichever comes first.
In December I would have over two years of regular warranty left, so rounding the months the five year extended warranty would only cover years 4-6 not 4-8. Am I reading this right? If so that works out to $439 per year (1,319/3) not to mention being uninsured in years 7 and 8.
The third quote was for purchasing at 30,000 miles which for me would likely be just before the 36 month regular warranty ends.
Code - Years - Mileage - Rate
F52 - 5 - 120,000 - $1,419.00
* Coverage for a Near New Honda vehicle begins on date of plan purhcase and expires at the end of plan terms or stated mileage, whichever comes first.
Since I would be near the end of the regular warranty the extended coverage would once again be for years 4-8. And the best deal at $283 per year (1,419/5)