It might take a few days to work out the kinks in the system, so
it's possible that some builds will get skipped, etc.
It would be rather convenient if instead of a date, you named the
tarballs after their commit hash. Eg:
pspp-47e6024280cbc95dbfa637009091cc8404c84fb0.tar.gz
I don't think that is a good idea. I don't expect a user telling in a list (s)he has found a bug in pspp-47e6024280cbc95dbfa637009091cc8404c84fb0. A date is more convenient to understand in what version (s)he found a problem. And it is more robust in finding a typo in the reported name.
What about generating a list in which every generated tarball with its commit hash is listed?
An other solution might be appending the latest commit hash to the currentname. Like pspp-merge-20081105-47e6024280cbc95dbfa637009091cc8404c84fb0.tar.gz.
If Ben can handle this automatic, users can refer the date and the developers can, if needed, check the list or the list with tarballs to find the commit hash belonging.
Have fun