I tried from midnight to 1:05am Eastern time, but could not check in for my NCL cruise. Got up at am and check in open. First check in window was 9-9:30am. But I wonder if they will really be open then, but if you want on 1st - maybe? I decided to sleep in in Athens and took a 11 - 11:30am window. A long cruise and no need to get on too early. Took about 10 minutes to complete (have to sit for 1 min video on safety). Have your passport info, credit card, emergency contact info, etc ready. You can take a pic with your phone or take one earlier and just upload from your PC or phone. Head shot.
Strange my NCL page said 21 days to cruise at 12:01 am, but would not open the check in section then.
I dont' think you can print the edocs until about a week ahead - they will email you when ready.