That was my experience also. I was the only one of the four traveling together who took the selfie. You are correct that they will retake the photo at the port. Why go through this online in the first place...RRR MSC's poor technology.
In reality, you can go whenever you wish to the port. Three years in a row (last time March 3) and no one asked to see the time on the docs. As someone else reported, the Seashore's muster drill is insane, with EVERYONE required to watch the video at the exact same time, call on the phone, and then run down to your muster station to verify. The crowds were insane and dangerous on the stairs as the elevators were locked/controlled. MSC needs to observe how other lines calmly stagger the muster throughout the day.