You guys found an issue that's gonna take longer than the 4 hours you've been shut down to fix?! What in the world could take an extra 2 hours?
The 4 hours is assuming everything goes according to plan. That time is used to deploy the update, other backend changes and checks to make sure it's all good.
During our checks, we discovered a critical issue that we needed to fix, and for us to address this before the servers go live we needed the extra time.