The Galaxy News Briefs provide information about what's included in each new Galaxy release - the page is here: http://wiki.galaxyproject.org/DevNewsBriefs, and a link to the page ia also available on the Galaxy News page here:http://wiki.galaxyproject.org/News.
Galaxy news Briefs are generally produced at the time that the release occurs, so they are not available prior to the release.
Regarding the dates of the release, the schedule is not strict, but generally every 2 months, with the release occurring on the first Monday of the month. The next release is currently scheduled for Monday, June 2, so tentative dates of upcoming releases will be the first Monday of August, the first Monday of October, etc. Again, these dates are tentative and can change based on circumstances.