The above posts are correct; however, we just cruised on Navigator OTS. We bought two bottles of vodka to take home with us, and we bought them probably around 10am on the last full day onboard. They just gave them to us to take with us. So we could have enjoyed at least one day of cheap imbibing but alas, we took the bottles home.
My understanding is that, anything prior to the last day, they will hold and deliver to your room on the last day.