how to limit recursive mirroring based on the directory modify time

I think that there is a limitation in lftp regarding  --newer-than
option - this seams to work only at file level.

I would like to stop lftp from entering old directories when it does
mirroring but I wasn't able to find a way for this.

Details: let's say that you have a folder where people are  dropping
daily builds and you want to mirror it. You know that a file
containing an old date is from an old build and it does not make sense
to continue recursion on it.

On in order words: how do I recursively mirror all sub-directories
that are newer-than a date for a given path?
Remark: these directories are quite big and it takes too much time for
lftp to scan them.

Thanks,
--
/sorin
http://nusunt.eu