Obviously in SAO anyone who was in the game on the first day was trapped inside. My question is, could someone on the outside a day (or whenever) later join in?

I would imagine it would be tempting for someone who had a significant other, child, someone, in the game or maybe they were depressed and thought SAO would lead to a better life.

I'm sure they would then become trapped themselves but is there anything stopping that inital jump after Akihiko Kayaba already trapped everyone?