Hello Ian!
Nicolas Huillard proposed the use of cron based scheduling of jobs.
This approach will overload you postgres server.
There is another solution, which I found, will give you the granularity
you will need:
you can combine cron based scheuling with the ability of batch job based
processing.
You can set up process queues which will allow to limit the number of
concurrent jobs running in this queue.
For further information, please contact http://www.gnqs.org
--
Mit freundlichen Gruessen / With best regards
Reiner Dassing