From the description this sounds more like the "feature lock" milestone of previous Bungie games (/most development cycles). In this 8 weeks they will focus the team on the remaining unfinished/unpolished features and get them finished. In this stage they'll stop creating new features and finish the ones they've already started - and figure out which ones can't be finished in time and cut them so that all focus goes into finishing the ones they can. The build at the end of the 8 weeks will basically be like the final game but they'll use the remaining time until launch to squash bugs / tune balance / polish assets. That build won't be quite ready for public consumption yet (even public beta worthy) - but it'll give everyone a static target to pour into cleaning up and polishing because they'll know that what's there won't be changing. All the art and music guys can also be more confident in finishing their pieces because they know it won't be changing and waste their time.