Changes introduced by commit 6b8e4d6e
were incomplete as not all time-sensitive checks were updated to match
revised "nta-lifetime" and "nta-recheck" values.  Prevent rare false
positives by updating all NTA-related checks so that they work reliably
with "nta-lifetime 12s;" and "nta-recheck 9s;".  Update comments as well
to prevent confusion.