$ hg log -G -r 'date("2014-08-22")'
On the MacPorts repo, that will result in a lot of changesets. For a
portfile, you really must specify a commit hash. In the
py-sphinx-contrib port, I use '0.0.YYYYMMDD' for the version. If the
project ever decides to tag a version, then that will be higher than the
one I made up. Also, it's clear from reading the version that it's a
made up one.