We've installed this feature in our 2.9.x (2.9.1) build of sakai, using the patch from
SAK-23812, and have discovered a possible bug:
When an assignment is duplicated, either by using an individual assignment's "duplicate" link, or by duplicating a site with assignments in it, attempting to edit the duplicate fails: in the UI, the user sees the warnings about editing an assignment after the end date, but remains on the assignment list, and a bug report is generated in tomcat's log because the code is attempting to insert a null date into the state (see attached log file).
I made a quick fix in AssignmentAction.java by only inserting the Peer Review date into the state if it's not null (see attached patch file). While this fixes the bug, making the assignment editable, it causes the peer review date selected by default to be unrelated to the new assignment's end date (for us, that's Jan 1, 2010). This could probably be addressed differently elsewhere in the code, though the best way to do so I'm not sure. Since the user is likely to have to tweak the dates of the assignment anyway, I'm not sure setting the peer review date is worth the effort.