This lets administrators reindex specific time ranges
according to git "approxidate" formats. These arguments
are passed directly to underlying git-log(1) invocations
and may still reach into old epochs.
Since these options rely on git committer dates (which we infer
from the most recent Received: header), they are not guaranteed
to be strictly tied to git history and it's possible to
over/under-reindex some messages. It's probably not a major
problem in practice, though; reindexing a few extra messages
is generally harmless aside from some extra device wear.
Since this currently relies on git-log, these options do not
affect -extindex, yet.