Your documents usually arrive about four weeks before your cruise. I have received documents less than a week after final payment and as close as three or four days before sailing.
Don't worry: If you fill in your online documentation, have your booking number, passport and credit card you'll be able to get on the ship. You REALLY don't need, hard copy, documents. The pier baggage handlers will be able to give you luggage tags that you can fill out at the pier. They have a manifest and can tell you your cabin number, if you don't know it.
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"There is a great difference between being well traveled and just having been to many places." ~Me