I think it's cleanest way :)
And if we can switch whispernet on it will be more simple way to correct date and time, but remember .. as the first line of the thread: it's about Kindle (
B002 &
B004) with U.S only wireless, and for other types in other places without wireless coverage.
So if wireless is working then all these steps are not needed.
Otherwise,
NTP synchronization before or after manual date modification will not cause any problem as you use it on any PC with any OS.