At the moment when you add a JIRA Project release event, it only includes the release date, for example
20 Oct 2014 to 20 Oct 2014
The 2nd date is greyed out, but if you change the 1st date to an earlier day it changes the 2nd one also. I believe this is due to the fact it won't span across multiple days.
With this changed, you could show the entire duration of a release cycle.