> 1) You should note that the execution time of a callout is O(log t)
>    with this structure.
...
> 3) The logic actually gets a bit simpler (in particular, you don't
>    have to do any distance tests when pulling entries up to a closer
>    bucket) if you have the bucket hierarchy extend to the end of time
>    (which is, IIRC, INT_MAX, because that's the maximum value hzto()
>    will return).

Actually, I have to correct myself.  If you have a truncated hierarchy
like you implemented, then it's actually still O(t), just with a big
constant factor (64*128) divided out.