I'm still saying early to mid June just because. My guts tell me that this version has bugs that will require that much and also the optimization part that is no small when you consider the dynamic and live world we are getting. Of course I hope it gets done earlier but whatever time it takes it's fine.
The worldgen machinery churns through game-centuries in a few minutes. I don't think a daily or weekly "tick" in the world is going to slow down the game noticeably (unless you are on a very marginal computer that constantly swaps everything in and out of virtual memory).
Yes, but you have to consider that there are various levels of abstraction and different things get computed depending on where you are. Worldgen is the uppermost level of abstraction. As you get closer to your adventurer, more things are calculated, for example whether or not there is someone talking with the leader of the site or where the various patrols in it are. Of course, not all things that happen in worldgen happen in adventure/fort mode, but this is offset by the fact that they have to be computed in greater detail because you are there (EDIT: or rather, you have the potential to be there), witnessing those events unfold.