I was thinking it would be around 5pm when we left. There are a few reasons why I thought this, but just speculation on my part.
1. Sunrise for Jan 7th is around 7:19am. We have guest ashore at 8:15 so we would need to be completely docked by 8:00am, so they need to start backing in the ship I would guess around 7:30. This isn't a lot of time for a daylight photo op. Whereas, sunset is around 5:43pm. We leave at 5pm and it's much easier and faster to leave the dock. The Magic would only be about an hour later leaving to go back to PC than it would be ig it stopped at CC that day.
2. The "stock" photos of the Magic and Wonder had both ships at sea. I don't see them taking a picture with the Wonder docked and other 2 at sea. I think it would look better if they were all lined up.
Guess we will just have to wait and see! But I'm also fairly certain we will know before we cruise. Disney would have to arrange the ariel photo shoot and I'm sure someone is going to leak the info. The higher ups already know what is happening, we just have to wait for it to trickle down to someone who just can't keep a secret.