- use DynamicList instead of List in the cache, which reduces the
  number of allocations occuring each time.

- since the cached times are stored in sorted order, first check if the
  new time is greater than the last list entry. Can then simply append
  without performing a binary search and can obviously also skip any
  subsequent sorting.

STYLE: add noexcept to Instant methods, declare in header (like Tuple2)