Hi,

For now, we can search releases by date :
http://musicbrainz.org/ws/2/release/?query=date:2014-08-21

Or even by timespan :
http://musicbrainz.org/ws/2/release/?query=date:[2014-08-18+TO+2014-08-24]

The same functionnality would be very handful for the release-groups (using the first release date).

Example :
I am currently developping an application that notify users when artists they like release an album.
Instead of browsing every day release-groups for every artist in my database (if there is 3000 artists, then it's 3000 browse requests to MB), I'd like to do just one request every day that checks new release-groups of the day, then I take only what I need.
Such a feature would allow me to do 1 request to MB instead of thousands every day.