Friends of ours did this, booking their cruise to join us at the last minute....just 3 days before sailing.
The pickup of documents at the port went very smoothly, the only problem is that you have to wait in the check in line, get the blank documents and get off the line to fill them out. Be sure to have your friends and family nearby to assist with the quick filling out of the documents! Then you have to get back in line a second time to actually check in. No problems at all, just a pain in the neck to have to fill it all out at the port and wait in line twice.
Go for it!